What do holes in volcanic rock illustrate about the conditions in which it was formed? ?

Some magma, which is called lava when it reaches the earth’s surface, is shot high into the air from pressure and gasses that accompany many eruptions. The air cools the magma and hardens it while it still contains the gasses that were present in the magma as bubbles. The resulting rock is filled with an infinity of holes which were once gas bubbles in the airborne lava.

2hydrogen and 1 covalent