Which of the following metals directly combine with hydrogen gas to give a hydride? — Hydrocarbons Chemistry Question

💡 Solution & Explanation

# Metals That Directly Combine with Hydrogen **Step 1: Identify which metals readily form hydrides** Metals that directly combine with hydrogen are those with: - High electronegativity (relative to hydrogen) - Strong ionic or covalent character in M–H bonds - Typically: alkali metals, alkaline earth metals, and some transition metals **Step 2: Evaluate common candidates** - **Alkali metals (Group 1)**: $Li, Na, K$ directly form hydrides ($LiH, NaH, KH$) ✓ - **Alkaline earth metals (Group 2)**: $Ca, Ba$ form hydrides ($CaH_2, BaH_2$) ✓ - **Transition metals**: Most do NOT directly combine with $H_2$ at normal conditions - **Metals like Cu, Ag, Pt**: Too noble; do not react directly ✗ **Step 3: Recognizing the pattern** Direct combination with $H_2$ occurs when: $$M + H_2 \rightarrow MH_x$$ This happens readily for **electropositive metals** (especially s-block elements), not noble or transition metals. --- **Why C is correct**: Without seeing the options, **C likely represents an alkali or alkaline earth metal** (such as Ca, Ba, Na, or K) that forms hydrides upon direct heating with hydrogen gas. These are the metals with sufficient reactivity to combine directly with $H_2$.