What is X in the sequence 4, 196, 16, 144, 36, 100, 64, X ?

Correct Answer: (B) 64

The sequence alternates between two interleaved patterns of perfect squares: the odd positions are $2^2 = 4, 4^2 = 16, 6^2 = 36, 8^2 = 64$; the even positions decrease by step of 2 in base: $14^2 = 196, 12^2 = 144, 10^2 = 100$. Following this decreasing even sequence, the next term $X$ at position 8 is $8^2 = 64$.