Biconditionals are statements that work both ways.
Some examples:
If it rains, I go out, and if I go out, it must be raining.
This can be stated concisely in mathematical terms as
I go out IF AND ONLY IF it rains.
So looking at the given statements, only the last two work both ways, namely:
If the sun rises in the east, then it is morning, and if it is morning, the sun rises in the east.
Victoria will play outside if and only if the weather is nice.
