Step 1: Understanding Electron Rich Hydrides:
Covalent hydrides are classified into three categories based on the availability of valence electrons relative to the number of bonds formed:
Electron-deficient: Have fewer electrons than required for writing a conventional Lewis structure (e.g., Group 13 hydrides like \( \text{B}_2\text{H}_6 \)).
Electron-precise: Have the exact number of electrons required to form covalent bonds with all substituents (e.g., Group 14 hydrides like \( \text{CH}_4 \)).
Electron-rich: Have excess electrons present as lone pairs (e.g., Group 15, 16, 17 hydrides).
Step 2: Analyzing the Options:
(A) \( \text{B}_2\text{H}_6 \), \( \text{AlH}_3 \): Group 13 elements. Electron-deficient.
(B) \( \text{NaH} \), \( \text{MgH}_2 \): Ionic hydrides (s-block elements).
(C) \( \text{HCl} \) (Group 17), \( \text{H}_2\text{S} \) (Group 16): These elements have lone pairs of electrons (Cl has 3, S has 2). Hence, they are electron-rich.
(D) \( \text{CH}_4 \), \( \text{SiH}_4 \): Group 14 elements. Electron-precise.
Step 3: Conclusion:
\( \text{HCl} \) and \( \text{H}_2\text{S} \) are electron-rich hydrides.