The binary equivalent of minus 15, using the two's complement system, is

Positive fifteen is 00001111, and its two's complement gives 11110001 for minus fifteen.

The value 11110000 is only the one's complement, missing the final adding of one.

The value 10001111 does not follow the two's complement steps at all.

None-of-these does not apply, since a valid value exists.

Two's complement is found by inverting all bits and then adding one.

The leading 1 marks the number as negative in signed form.