What is described in the following equation?

2H2 (g) + O2 (g) → 2H2O (l)

A.

hydrogen gas combining with oxygen gas to form water

B.

hydrogen gas combining with water gas to form hydroxide

C.

water decomposing to oxygen gas and hydrogen gas

D.

helium gas combining with oxygen gas to form water

A. Hydrogen gas combining with oxygen gas to form water.

Explanation:

H2 is the symbol for Hydrogen in gaseous state and O2 is the symbol for Oxygen in gaseous state. H2O is the chemical formula of Water. It is clearly indicated in the equation that Hydrogen and Oxygen combining to form Water.

The arrow to the water indicate that the water is the product and it is NOT the decomposition reaction.