Answer:
Binomial distribution because:
Trials are Bernoulli (affected or not)
Probability is known (p=0.05) and remains constant for all trials.
Number of trials is known (n=6).
P(x)=C(n,x)p^x*(1-p)^(n-x)
x=0 =>
P(0)=C(6,0)(0.05^0)(0.95^6)
=0.7351.... (approximately)