Correct Option: C

As per given series , we can see that
First term = 1
Second term = First term × 2
⇒ Second term = 1 × 2 = 2
Similarly we can find the all others terms
Third term = Second term × 3
⇒ Third term = 2 × 3 = 6
Fourth term = Third term × 4
⇒ Fourth term = 6 × 4 = 24
Fifth term = Fourth term × 5
⇒ Fifth term = 24 × 5 = ?
∴ ? = 120
Sixth term = Fifth term × 6
⇒ Sixth term = 120 × 6 = 720