Both reactions yield Ca(OH)2 and H2 with water

Steps:

• Calcium reacts with water: Ca + 2H2O → Ca(OH)2 + H2, producing white solid Ca(OH)2 and colorless gas H2.
• Calcium hydride reacts with water: CaH2 + 2H2O → Ca(OH)2 + 2H2, producing same white solid Ca(OH)2 and colorless gas H2.
• Both reactions share the identical white solid, calcium hydroxide.
• The colorless gas is hydrogen in each case, matching the description.

Why A is correct:

• Balanced equations confirm both produce H2 gas and Ca(OH)2 solid from water.

Why the others are wrong:

• B: Neither reaction generates O2; H2 displaces from H2O.
• C: Ca produces H2, not O2.
• D: CaH2 produces H2, not O2.

Final answer: A