CBSE Class 10 Answered

It is rare, but possible.

All organisms result from the random combining of only certain underlying genotype of the parents. That is how meiosis works. 

Certain dark-skinned people have genes for fair complexion as well as genes for dark complexion. So the father produces some sperms at random with light genes and some sperms with dark genes. And the mother has some ova with light genes and some with dark. If a dark-gene sperm happens to fertilize a dark-gene egg, the kid comes out darker than both parents. If a light-gene sperm happens to fertilize a light-gene egg, the kid comes out lighter than both parents. If a dark-gene sperm happens to fertilize a light-gene egg, or vice-versa, the kid comes out about the same as both parents.

And so, the probability of a child coming out lighter than both parents is 1/4. The probability of a child coming out darker than both parents is also 1/4.