Correct Answer: 9876

Solution : Given:
11, 12, 26, 81, 328, 1645, ?

In the above-given series, starting from 1, multiply the consecutive numbers with each term, and then add those consecutive numbers to the resultant to find the next term.
11→(11 × 1) + 1 = 11 + 1 = 12
12→(12 × 2) + 2 = 24 + 2 = 26
26→(26 × 3) + 3 = 78 + 3 = 81
81→(81 × 4) + 4 = 324 + 4 = 328
328→(328 × 5) + 5 = 1640 + 5 = 1645
1645→(1645 × 6) + 6 = 9870 + 6 = 9876

So, 9876 is the missing term of the given series. Hence, the second option is correct.