(c)
Given that,
$\lambda = 229\ pm\$and$\ \theta = 23{^\circ}20'$
Substituting these values in the Bragg’s equation, we have
$d_{hkl} = \frac{\lambda}{2\sin\theta} = \frac{229\ pm}{2\sin{(23{^\circ}20')}}$
$= \frac{229\ pm}{2 \times \ 0.396}$
= 289.2 pm