Q: How many electrons can fit in the third energy level ($n=3$) of an atom?

$2n^2 = 2 \times 3^2 = 18$ electrons

Question 1

Which of the following statements best describes the relationship between wavelength ($\lambda$), frequency ($
u$), and the speed of light ($c$) for electromagnetic radiation?

Accepted Answer

$c = \lambda 
u$

Question 2

A photon is absorbed by a hydrogen atom, causing an electron to move from $n=2$ to $n=4$. Which of the following is true about the energy and wavelength of the photon?

Accepted Answer

The photon has positive energy and a wavelength corresponding to the energy difference between $n=2$ and $n=4$.

Question 3

Which subatomic particle is primarily responsible for determining the chemical behavior of an atom?

Accepted Answer

Electron

Question 4

How many electrons can fit in the third energy level ($n=3$) of an atom?

Accepted Answer

$2n^2 = 2 	imes 3^2 = 18$ electrons

Question 5

Which of the following electron configurations is correct for the element sulfur (S, atomic number 16)?

Accepted Answer

$1s^2 2s^2 2p^6 3s^2 3p^4$

Question 6

Which of the following best explains why atomic size decreases from left to right across a period in the periodic table?

Accepted Answer

Increasing nuclear charge pulls electrons closer to the nucleus.

Question 7

What is the correct name for the compound $Fe_2O_3$?

Accepted Answer

Iron (III) oxide

Question 8

Which of the following is the empirical formula for glucose ($C_6H_{12}O_6$)?

Accepted Answer

$CH_2O$

Question 9

A sample contains $3.01 	imes 10^{23}$ molecules of $CO_2$. How many moles of $CO_2$ are present?

Accepted Answer

$0.5$ moles

Question 10

Which of the following compounds contains a polyatomic ion?

Accepted Answer

$Na_2SO_4$

Question 11

What is the molar mass of $Ca(NO_3)_2$? (Atomic masses: Ca = 40.08 g/mol, N = 14.01 g/mol, O = 16.00 g/mol)

Accepted Answer

$164.10$ g/mol

Question 12

Which of the following best describes the Pauli exclusion principle?

Accepted Answer

No two electrons in the same atom can have the same set of four quantum numbers.

Question 13

Which of the following elements has the highest ionization energy?

Accepted Answer

Fluorine

Question 14

What is the correct formula for magnesium nitride?

Accepted Answer

$Mg_3N_2$

Question 15

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

$CH_2O$

Question 16

Which of the following is the correct abbreviated electron configuration for chlorine (Cl, atomic number 17)?

Accepted Answer

$[Ne] 3s^2 3p^5$

Question 17

Which of the following best describes why metals tend to form cations in ionic compounds?

Accepted Answer

Metals have low ionization energies and lose electrons to achieve a stable octet.

Question 18

How many moles of hydrogen atoms are present in $2$ moles of $C_2H_6$?

Accepted Answer

$12$ moles

Question 19

Which of the following is the correct name for $Na_2CO_3$?

Accepted Answer

Sodium carbonate

Question 20

A compound has an empirical formula of $CH_2$ and a molar mass of $56$ g/mol. What is its molecular formula? (C = 12 g/mol, H = 1 g/mol)

Accepted Answer

$C_4H_8$

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