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25, 100, ?, 1600, 6400
A.  400
B.  300
C.  360
D.  420
E.  None of these

Here,the number is multiplied by 4 successively to get the next result.

$25 \times 4 =100$

$100 \times 4 =400$

$400 \times 4 =1600$

$1600 \times 4 =6400$

Hence,Option(A)$400$ is the correct choice.
The given series is completely divisible series each number is div by 4 hence

the options A) 400 is correct