The correct option is D 8
We know that, the coefficient of the middle term is the numerically greatest coefficient in the expansion of (1+x)n or (1+x)n and its value is nCn/α or nCn+12=nCn−12 according as n is even or odd.
It is given that the coefficient of the 5th term is the greatest. Therefore, 5th term is the middle term. Thus, there are 9 terms. Hence, n=8.