A science question about Lava

This is for my grandchild can you be of help.. Thank you. Here is the question

A blob of lava erupts from a volcano and lands in the ocean. What kind of rock will form from it?

Here are the choices she has to pick from

a.) sedimentary with many sizes of grain
b.) sedimentary with one size of grain
c.) igneous with small crystals
d.) igneous with large crystals

Once again thank you

The answer is "c" - igneous with small crystals. But, make sure your grandchild understands why. The why is that when molten materials cool quickly they produce many centers for crystallization. Thousands and thousands would form within a blob of lava that lands in the ocean. Each of these centers becomes a small crystal instead of a few large ones.

You didn't ask this but... if the molten material cools slowly, like deep underground, a few centers of crystallization would form and the crystals would grow slowly because they are prevented from cooling quickly by all of the insulation rocks around. The result would be a few large crystals.

c.) igneous with small crystals