If both parents are carriers for thalassaemia, which is autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child?

The correct option is A 25%
Suppose, N is the normal gene and $N^T$is the carriers gene for thalassaemia.

Gametes from parents	N	$N^T$
N	NN	N$N^T$
$N^T$	N$N^T$	$N^T$$N^T$

Since thalassaemia is autosomal recessive disorder, the chances (percentage) of pregnancy resulting in an affected child
= $\frac{1}{4}\times 100$%
= 25%