Based on the chemical principles of ionic bonding and charge neutrality, the charge of X in the formula XN must be +3, (B).
What is the right chemical formula?
In a correctly written chemical formula, the sum of the charges of all the atoms in the molecule must be equal to zero.
N in XN contributes a charge of -3.
To achieve a neutral molecule (charge of 0), X must have a charge of +3 to compensate for the negative charge of N.
Therefore, since N has a charge of -3 (nitrogen is a trivalent anion), X must have a charge of +3 to balance the formula.
Complete question:
What must the charge of X be if it is written correctly as XN?
O
+3
+1
O
-1