The mass of $10^{21}$ atoms of $Cu$ is ..... grams.

The ratio of the number of oxygen atoms $(O)$ in $16.0 \ g$ ozone $(O_3)$,$28.0 \ g$ carbon monoxide $(CO)$,and $16.0 \ g$ oxygen $(O_2)$ is (Atomic mass: $C = 12$,$O = 16$ and Avogadro's constant $N_A = 6.0 \times 10^{23} \ mol^{-1}$)

Find the number of moles of sodium atoms in $6.9 \times 10^{-2} \ kg$ (Atomic mass $= 23 \ g \ mol^{-1}$)

What is the number of $CO_2$ molecules in $45.42 \ L$ at $\text{STP}$? (Consider molar volume of gas at $\text{STP} = 22.71 \ L \ mol^{-1}$)

Calculate the number of valence electrons in $4.2 \ g$ of $N_3^-$ ions in terms of $N_A$ ($N_A$ = Avogadro constant). (in $N_A$)

What is the volume occupied by $16 \ g$ methane gas at $STP$ (in $cm^3$)?