Answer: The correct option is (b) 312.
Step-by-step explanation: We are given to use formula to find the sum of first four terms of the following geometric sequence :
2, 10, 50, . . .
We know that
the sum of first n terms of a geometric sequence with first term a and common ratio r is given by

For the given geometric sequence, we have
first term, a = 2
and the common ratio, r is given by

Therefore, the sum of first four terms of the given geometric sequence is

Thus, the required sum of first four terms is 312.
Option (b) is CORRECT.