Complete the series: a, c, e, g, ?

B. H

What is the missing number in the series: 2, 6, 12, 20, ?, 42

B. 32

Identify the missing number in the series: 1, 4, 9, 16, ?, 36

A. 25

What is the missing number in the series: 100, 90, 80, 70, ?, 50

A. 60

Find the missing letter in the series: b, d, f, h, ?

A. J