(b) 7
Since probability of any event must satisfy $0 \leq P(E) \leq 1$, the value 7 exceeds 1 and hence cannot be a probability.
Source: Chapter 14, Section 14.2 Summary
The key rule is $0 \leq P(E) \leq 1$. Check each option: 0 is valid (impossible event), 0.01 is between 0 and 1, and $\frac{0.07}{3} \approx 0.023$ is also between 0 and 1. Only 7 exceeds 1, making it impossible as a probability value. Examiners expect you to state the rule and identify the violating option.