2) B

This question deals with valencies.

X, being in group 3, has a valency of +3. It has 3 electrons in its outer shell. It needs to donate its 3 electrons to be stable.

Y is in group 6, meaning it needs 2 electrons to be stable. Its valency is -2.

To find the formula we can use the following technique:

X Y

X

+3 -2

The big X is a criss cross, meaning -2 goes to X and +3 goes to Y.

So the formula is X₂Y₃.

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