What is a biconditional statement for the moon is the largest satellite of earth

The moon is the largest satellite if and only if it is for earth.

A combination of conditional and converse part of a statement is termed as biconditional statement. In mathematics , there is logic to put "if and only if" between the statement so the statement would be true from the both sides(conditional and converse) of the statement.

For example:  Biconditional statement for statement ab is "a if and only if b" where a is hypothesis and b is result.