For the case of $^4He_2$ atoms, the number of ways the atoms can occupy different energy levels is given by the number of ways to assign two atoms to two distinct levels, which is $\binom{4}{2} = 6$.
For $^3He_2$ atoms, the number of ways the atoms can occupy different energy levels is similar, but there is an additional restriction due to the quantum nature of the system. After solving for the probabilities $p$ and $q$, we find that:
\[
\frac{p}{q} = 0.6.
\]
Thus, the correct answer is (A) 0.6.