If the probability of seeing an exponent question on a particular stan

We'll try going for a direct calculation as the numbers look very simple.
This is a Precise approach.

Instead of calculating directly, we'll try calculating the probability of not seeing an exponent.
Not seeing an exponent has a probability of 1 - 0.05 = 0.95
So if we don't see an exponent twice our probability is 0.95*0.95 and our desired probability is 1 - 0.95*0.95
This isn't a very friendly calculation and we can solve it in two ways:
Using the identity (a-b)^2: 1 - 0.95*0.95 = 1 - (1-0.05)^2 = 1 - (1 - 0.1 +0.0025) = 1 - 0.9025 = 0.0975
Estimating: multiplying by 0.95 is like multiplying by 95% or taking off 5%. 5% of 95 is about 5 so 95% of 95 is about 90.
so 0.95*0.95 is about 0.9 and our answer is about 1 - 0.9 = 0.1. Only (B) fits.
(B) is our answer.

A different, less calculation intensive approach to solution is Logical:
The probability for seeing an exponent in the first question is 5%.
Therefore the probability for seeing it in the first or the second question must be greater than 5%.
Only (A) 50% and (B) 9.75% are larger than 5%.
(A) is way too large so our answer must be (B).