The correct option is
B 10−12m
The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American spelling) is a unit of length in the metric system, equal to 1×10−12 m, or one trillionth (11000000000000) of a metre, which is the SI base unit of length.
Hence, the correct option is C