5. Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for a 10.0
mg sample to decay and have only 1.25 mg of it remain?

Answer:

Because the compound has a formula of M2O, the number of valence electrons of M should be 1. Therefore, (1) Group 1 is the correct answer because elements in group 1 have 1 valence electron.

Explanation:

Answer:

1413.386

Explanation:

Since, the options have not been given the question is incomplete.

What is Darwin's name for species that do not appear to have changed for millions of years?

a.

Dinosaurs

b.

Living fossils

c.

Old souls

d.

Ancient moderns

Answer: b. Living fossil

Explanation:

In 1859 Charles Darwin proposed the term living fossil, that means a species or group of species that had not changed in terms of evolutionary context thus can be useful in tracing the extinct or previously existing forms of life. The examples of the living fossils are horseshoe crabs, ginkgo (Conifers) and tuatara. These group of animals were existed unchanged in the Ordovician, Permian, and Triassic periods respectively with few surviving species.

Answer:

the answer is living fossils so it would be b

Explanation:

how do i know i took the test

Answer:

36 electrons

Explanation:

The # of protons is always equal to the atomic number. In the case of Sr (Strontium), it is 38 protons.

The 2+ at the end means that it has a charge of +2, meaning that it LOST two electrons to become a cation with a full valence shell. So, 38 - 2 = 36 electrons

Answer:

38 protons 36 electrons 30 neutron because of 29 isotope

Answer: $6,600[tex]\alpha \sqrt[n]{x} \lim_{n \to \infty} a_n[/tex]

Explanation:

Answer:

kinetic energy I think so

The form of energy molecules have at the molecular level is Kinetic energy.

Kinetic energy is defined as the energy possessed by a body as a result of its motion or movement.

Molecules interact with one another through various movements that occur

within them. This happens to aid the formation of new substances in the

ecosystem. The three states of matter exhibit varying degree of movement

within its molecules.

The energy is usually in the form of chemical energy also and is the reason

why kinetic energy is the most suitable choice.

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Answer: The empirical formula of X  is [tex]Cr_2O_3[/tex]

Explanation:

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of Cr = 68.4 g

Mass of O = 31.5 g

Step 1 : convert given masses into moles.

Moles of Cr =[tex]\frac{\text{ given mass of Cr}}{\text{ molar mass of Cr}}= \frac{68.4g}{52g/mole}=1.31moles[/tex]

Moles of O =[tex]\frac{\text{ given mass of O}}{\text{ molar mass of O}}= \frac{31.5g}{16g/mole}=1.97moles[/tex]

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For Cr = [tex]\frac{1.31}{1.31}=1[/tex]

For O = [tex]\frac{1.97}{1.31}=1.5[/tex]

The simple whole number ratio of Cr : O= 2: 3

Hence the empirical formula is [tex]Cr_2O_3[/tex]

Answer:

C)2 mole Cu(NO3)2 / 2 mole Fe

Explanation:

I'm pretty sure.

When iron is combined with copper (1) nitrate, it produces iron (II) nitrate and copper. The following could NOT be a mole ratio in this chemical reaction is:

D) 1 mole Fe(NO₃)₂ / 1 mole Fe

To determine which of the given mole ratios could NOT be part of the chemical reaction between iron and copper(1) nitrate, we need to write the balanced chemical equation for the reaction and then compare it to the given ratios.

The balanced chemical equation for the reaction is:

Fe + Cu(NO₃)₂ → Fe(NO₃)₂ + Cu

A) 1 mole Fe / 2 mole Cu

This mole ratio is consistent with the balanced chemical equation, where 1 mole of Fe reacts with 2 moles of Cu(NO₃)₂ to produce 1 mole of Fe(NO₃)₂ and 1 mole of Cu. So, this ratio could be part of the chemical reaction.

B) 1 mole Fe(NO₃)₂ / 2 mole Cu

This mole ratio is also consistent with the balanced chemical equation, where 1 mole of Fe(NO₃)₂ is produced by reacting 2 moles of Cu(NO₃)₂. So, this ratio could be part of the chemical reaction.

C) 2 mole Cu(NO₃)₂ / 2 mole Fe

This mole ratio is consistent with the balanced chemical equation, where 2 moles of Cu(NO₃)₂ react to produce 2 moles of Fe(NO₃)₂. So, this ratio could be part of the chemical reaction.

D) 1 mole Fe(NO₃)₂ / 1 mole Fe

This mole ratio implies that 1 mole of Fe(NO₃)₂ is produced by reacting with 1 mole of Fe, which is not consistent with the balanced chemical equation. The equation shows that 1 mole of Fe reacts with 1 mole of Cu(NO₃)₂ to produce 1 mole of Fe(NO₃)₂ and 1 mole of Cu. Therefore, this ratio could NOT be part of the chemical reaction.

So, the correct answer is:

D) 1 mole Fe(NO₃)₂ / 1 mole Fe

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Answer: physically

Explanation: it's a physical change because the air that fills it up does not affect its chemical compound like I'd you mix metal in salt water

Answer:

Option B. Plutonium-243

Explanation:

To know the the correct answer to the question, we shall write the balanced equation for the reaction showing curium-247 (²⁴⁷Cm) emitting alpha particle. This is illustrated below:

²⁴⁷₉₆Cm —> ᵐₙX + ⁴₂He

Next, we shall determine m, n and X. This can be obtained as follow:

247 = m + 4

Collect like terms

247 – 4 = m

243 = m

Thus, m is 243

96 = n + 2

Collect like terms

96 – 2 = n

94 = n

Thus, n is 94

m = 243

n = 94

ᵐₙX => ²⁴³₉₄X => ²⁴³₉₄Pu

Thus, the equation is:

²⁴⁷₉₆Cm —> ²⁴³₉₄Pu + ⁴₂He

From the illustrations above, the daughter nuclei formed is Plutonium-243 (²⁴³₉₄Pu)

Answer:

Plutonium-243

Explanation:

Answer:

By bonding due to the attractive forces

Answer:

In gases are much more spread out than in solids or liquids. They vibrate and move freely at high speeds. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

Explanation:

In the image shown above, there are 3 elements (option C).

Element is one of the simplest chemical substances that cannot be decomposed in a chemical reaction or by any chemical means and made up of atoms all having the same number of protons.

As stated above, all elements are made up of backbone structures called atoms. The atoms of an element are the same.

According to this question, an image is given showing atoms of different colors. Each atom with the same color belongs to a single element.

Since there are there colors, this means that there are three elements in the picture.

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Answer: The empirical formula is [tex]H_4P_2O_7[/tex]

Explanation:

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of H= 2.270 g

Mass of P = 34.80 g

Mass of O = 62.93 g

Step 1 : convert given masses into moles

Moles of H =  [tex]\frac{\text {given mass}}{\text {Molar mass}}=\frac{2.270g}{1g/mol}=2.270[/tex]

Moles of P =  [tex]\frac{\text {given mass}}{\text {Molar mass}}=\frac{34.80g}{31g/mol}=1.122[/tex]

Moles of O = [tex]\frac{\text {given mass}}{\text {Molar mass}}=\frac{62.93g}{16g/mol}=3.933[/tex]

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For H =  [tex]\frac{2.270}{1.122}=2[/tex]

For P=    [tex]\frac{1.122}{1.122}=1[/tex]

For O =   [tex]\frac{3.933}{1.122}=3.5[/tex]

The simples ratio will be = H: P : O= 4: 2: 7

Hence the empirical formula is [tex]H_4P_2O_7[/tex]

Answer:

4.99*10²³ molecules of N₂O₄ are in 76.3 g of N₂O₄

Explanation:

Avogadro's Number is the number of particles that make up a substance (usually atoms or molecules) and that can be found in the amount of one mole of said substance. Its value is 6.023*10²³ particles per mole. Avogadro's number represents a quantity without an associated physical dimension. Avogadro's number applies to any substance.

You know that the molar mass of N₂O₄ is 92.02 g/mol, and you have 76.3 g. Then you can apply the following rule of three: 92.02 grams are present in 1 mole of the compound, 76.3 grams in how many moles are they?

[tex]amount of moles= \frac{76.3 grams*1 mole}{92.02 grams}[/tex]

amount of moles= 0.83 moles

Then, you can apply another rule of three: if by definition of Avogadro's number 1 mole of the compound has 6.023*10²³ molecules, 0.83 moles of the compound, how many molecules will it have?

[tex]amount of molecules= \frac{0.83 moles*6.023*10^{23}molecules }{1 mole}[/tex]

amount of molecules= 4.99*10²³

4.99*10²³ molecules of N₂O₄ are in 76.3 g of N₂O₄

Answer:

I hope this helps!Good luck

Pounds of gold ore :  11,02311

Given

5 g of gold

0.1% gold by mass

Required

Pounds of gold ore

Solution

[tex]\tt \%mass~gold=\dfrac{mass~gold}{mass~ore}\times 100\%[/tex]

For percent mass = 0.1%, than mass of gold ore :

[tex]\tt 0.1\%=\dfrac{5~g}{mass~ore}\times 100\%\\\\mass~ore=\dfrac{5\times 100}{0.1}\\\\mass~ore=5000~g[/tex]

Conversion factor :

1 g = 0,00220462 pound, than for 5000 g = 11,02311 pounds

Answer:

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Answer:

A because it is not small enough

Explanation:

It's a of c Yea a or so pick that

Answer:

Increase

Explanation:

Hope it helps you

Answer:

Decrease

Explanation:

If the oil you're referring to is just some normal oil, it'll lessen the friction and cause it to side more smoothly

Answer:

[tex]C_{4}H_{10}O[/tex]

Explanation:

Hello!

In this case, since the empirical formula of compounds whose by-mass compositions are known, is computed by first computing the moles considering those compositions as actual masses:

[tex]n_C=\frac{64.82g}{12.01g/mol}=5.40mol\\\\n_H=\frac{13.62g}{1.01g/mol}=13.5mol\\\\n_O=\frac{21.58g}{16g/mol}=1.35mol[/tex]

Next, we divide each moles by the fewest ones, in this case those of oxygen to obtain the subscript in the empirical formula:

[tex]C=\frac{5.40}{1.35}= 4\\\\H=\frac{13.5}{1.35}=10\\\\O=\frac{1.35}{1.35}=1[/tex]

Thus, we obtain:

[tex]C_{4}H_{10}O[/tex]

Best regards

Answer:

Explanation:

So chemical changes require a change on a molecular level that cannot be reversed because they form some new substance. Souring milk is not something you can reverse, and the process of it souring produces new molecules.

2Ag⁺(aq) + Mg(s)→ 2Ag(s) + Mg²⁺ (aq)

Given

Standard cell notation:

Mg(s) | Mg2+ (aq) || Ag+(aq)| Ag(s)

Required

a balanced redox reaction

Solution

At the cathode the reduction reaction occurs, the anode oxidation reaction occurs

In reaction:  

Ag⁺ + Mg → Ag + Mg²⁺  

half-reactions

Ag⁺ (aq) + e⁻ ---> Ag (s)  x2

2Ag⁺ (aq) + 2e⁻ ---> 2Ag (s)

Mg (s) → Mg²⁺ (aq) + 2e−

a balanced cell reaction

2Ag⁺(aq) + Mg(s)→ 2Ag(s) + Mg²⁺ (aq)

Answer:2Ag⁺(aq) + Mg(s)→ 2Ag(s) + Mg²⁺ (aq)

Explanation:

just took test

The given question is incomplete. the complete question is : If 5.15 g[tex]Fe(NO_3)_3[/tex] is dissolved in enough water to make exactly 323 ml of solution, what is the molar concentartion of nitrate ion.

Answer:  The molar concentartion of nitrate ion is 0.195.

Explanation:

Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.

Given : 5.15 g of [tex]Fe(NO_3)_3[/tex] is dissolved

Volume of solution = 323 ml

[tex]Molarity=\frac{n\times 1000}{V_s}[/tex]

where,

n= moles of solute

[tex]Moles=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{5.15g}{242g/mol}=0.021moles[/tex]  

[tex]V_s[/tex] = volume of solution = 323 ml

[tex]Molarity=\frac{0.021\times 1000}{323}=0.065M[/tex]

As 1 M of [tex]Fe(NO_3)_3[/tex] gives 3 M of [tex]NO_3^-[/tex] ions.

Thus 0.065 M of [tex]Fe(NO_3)_3[/tex] gives  = [tex]\frac{3}{1}\times 0.065=0.195M[/tex] of [tex]NO_3^-[/tex] ions.

The molar concentartion of nitrate ion is 0.195.

Answer:

6200 meters

Explanation:

To convert from km to m you have to multiply the number by a thousand

Answer:

6.2×10^3 m

Explanation:

6.20×1000=6200m

In scientific notation 6200 = 6.2×10^3

Answer:

5.44 moles of nitrogen required.

Explanation:

Given data:

Number of moles of NH₃ = 10.88 mol

Moles of N₂ required = ?

Solution:

Chemical equation:

N₂ +  3H₂         →       2NH₃

Now we will compare the moles nitrogen and hydrogen.

               NH₃          :           N₂

                 2             :           1

               10.88        :         1/2×10.88 = 5.44mol

5.44 moles of nitrogen required.

Answer:

348.9 mL of the 60% solution and 251.1 mL of the 15% solution.

Explanation:

First, we calculate how many mililiters of pure carbonic acid are there in 650 mL of a 38% solution:

Then we can express the sum of both initial solutions as:

for the volume of carbonic acid; and

For the volume of the solutions.

We now have a system of two equations and two unknowns (x is the volume of the 60% solution and y is the volume of the 15% solution).

We express x in terms of y in equation 2):

And replace x in equation 1):

Finally we calculate x using equation 2):

Answer:

MARK AS BRAINLIEST

Explanation:

Boron trifluoride only has six valence electrons and is one of the relatively rare second period covalent molecules that disobeys the octet rule. There are three bonded groups and so no lone pairs. Six electrons implies three electron pairs and therefore a trigonal geometry.

3 bonding and 0 non-bonding electron pairs are found in the BF3 molecule.

Chemical Bonding refers to the formation of a chemical bond between two or more atoms, molecules, or ions to give rise to a chemical compound.

Boron trifluoride only has six valence electrons and is one of the relatively rare second-period covalent molecules that disobeys the octet rule.

There are three bonded groups and so no lone pairs. Six electrons imply three electron pairs and therefore a trigonal geometry.

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