If $\square \square \square \square \square \square$ stands for 300, what does $\square \square$ stand for?

The correct option is B 100
If $\square \square \square \square \square \square$ stands for 300, it means six squares represent 300.

So, one $\square$ represents $\frac{300}{6}$.

one $\square$ represents $50$.

Thus, $\square \square$ represent = $2\times 50=100$.