Textbook Problem

For each of the following molecules or ions, indicate the bond angle expected between the central atom and any two adjacent hydrogen atoms.

msp;  $\begin{array}{l}\text{a}.{\text{ H}}_{\text{2}}\text{O} \\ \text{b}.{\text{ NH}}_{\text{3}} \\ \text{c}.{\text{ NH}}_{\text{4}}{}^{+}\\ \text{d}.{\text{ CH}}_{\text{4}}\end{array}$