Question

If the edge length of an NaH unit cell is $488$ pm, what is the length of an Na-H bond if its crystal has fcc structure?

• A. $488$ pm
• B. $122$ pm
• C. $244$ pm
• D. $976$ pm

Answer 1

The correct option is C $244$ pm

Length of an $Na-H$ bond $=r_{+}+r_{-}$

$\because 2\left(r_{+}{+r}_{-}\right)=a$(edge length)

$\because 2\left(r_{+}{+r}_{-}\right)=488pm$
The length of Na-H bond is the interatomic separation between $N{a}^{+}$ and $H^{-}$ ions

$\therefore r_{+}+r_{-}=244pm$