When the index level and strike price of a listed index option are the same,...

An option is considered "at the money" when the current price of the underlying asset (or index level) equals the option’s strike price.

B is correct because the index level equals the strike price.

A is incorrect because "in the money" requires the option to have intrinsic value (e.g., for a call, the index level must be above the strike price).

C is incorrect because "out of the money" applies when the index level is below the strike price (for calls) or above it (for puts).

D is incorrect because "at the money" options have no intrinsic value.