Complete the following statements :
The probability of an event that cannot happen is _______ Such an event is called

Answer

To complete the statements, we will analyze the concepts of probability related to events that cannot happen.

### Step-by-Step Solution:

1. **Understanding Probability**:
- Probability is a measure of the likelihood of an event occurring. It is calculated as the ratio of the number of favorable outcomes to the total number of possible outcomes.

2. **Identifying the Event**:
- An event that cannot happen means there are no favorable outcomes for that event. For example, if we are rolling a standard die, the event of rolling a 7 is impossible because a die only has numbers 1 through 6.

3. **Calculating the Probability**:
- The probability of an event is given by the formula:
\[ P(E) = \frac{n(E)}{n(S)} \]
where \( n(E) \) is the number of favorable outcomes for the event, and \( n(S) \) is the total number of possible outcomes.

4. **Applying to Impossible Events**:
- For an impossible event, \( n(E) = 0 \) because there are no outcomes that can satisfy the event. Therefore, the probability becomes:
\[ P(E) = \frac{0}{n(S)} = 0 \]

5. **Defining the Event**:
- An event that has a probability of 0 (cannot happen) is referred to as an "impossible event".

### Final Statements:
- The probability of an event that cannot happen is **0**.
- Such an event is called **impossible event**.