The answer is B: Large group with different risks.
Explanation for each option:
A. Excluded catastrophic perils - This is correct because insurable risks typically exclude catastrophic perils that could cause widespread losses, as these are difficult to predict and insure against.
B. Large group with different risks - This is incorrect because insurable risks require a large group with similar risks, not different risks. Insurance relies on pooling similar risks to predict losses accurately and set premiums.
C. Calculable chance of loss - This is correct because for a risk to be insurable, the chance of loss must be calculable. This allows insurers to set appropriate premiums based on the likelihood of a loss occurring.
D. Accidental losses - This is correct because insurable risks must involve accidental losses. Insurance is designed to protect against unforeseen and unintended events, not deliberate actions.
In summary, option B is the exception because insurable risks require a large group with similar, not different, risks.