How Many Molecules Are in (A) $1.0 \mathrm {~cm} ^ { 3 }$

Short Answer

How many molecules are in (a) $1.0 \mathrm {~cm} ^ { 3 }$ of air at STP and (b) $1.0 \mathrm {~cm} ^ { 3 }$ of helium at STP? (R
$\left. = 8.31 \mathrm {~J} / \mathrm { mol } . \mathrm { K } , N _ { \mathrm { A } } = 6.022 \times 10 ^ { 23 } \mathrm { molecules } / \mathrm { mol } \right)$