The correct option is A 51
(x+a)100+(x−a)100
Applying binomial theorem for expansion of the following
(x+a)100+(x−a)100
=x100+x99(100C1a)+x98(100C2a2)...(100C100a100)
+x100−x99(100C1a)+x98(100C2a2)...(100C100a100)
=2[x100+x98(100C2a2)+x96(100C4a4)...(100C100a100)]
The powers of a are in A.P
a0,a2,a4,a6...a100
0,2,4,6...100
Hence, including the term a0orx100 there are 51 terms.