(a)[2]
State what the Avogadro constant $N_A$ means.
(b)[4]
A balloon contains helium gas at a pressure of $1.1 \times 10^{5}\ \text{Pa}$ and a temperature of $25^\circ\text{C}$. Its volume is $6.5 \times 10^{4}\ \text{cm}^3$. Helium can be treated as an ideal gas. Find the number of gas atoms in the balloon.