__H2 + __O2 --> __H2O If 42.3 moles of water are produced, how many moles of hydrogen gas was reacted?

42.3moles

Explanation:

The chemical equation given in this question is as follows:

H2 + O2 → H2O

However, this equation is unbalanced, the balanced chemical equation is as follows:

2H2 + O2 → 2H2O

This equation shows that;

2 moles of hydrogen gas (H2) will produce 2 moles of water (H2O)

Hence, If 42.3 moles of water (H2O) are produced, 42.3 × 2/2

= 42.3moles of hydrogen was reacted.

it is the most commonly accepted one