Final answer:
The oxidation state of the unknown element X in the compound XCl is +1, as chlorine has a -1 charge and the total charge of the compound must be neutral.
Step-by-step explanation:
To determine the oxidation state of the unknown element X in the compound XCl, we can use the known oxidation state of chlorine and the rule that the sum of oxidation states in a neutral compound must be zero. Chlorine, being a halogen, generally has an oxidation state of -1 when it forms halide compounds. Given that the compound XCl is neutral, if chlorine is Cl-, then X must balance it with a positive charge. The unknown element X must have an oxidation state of +1 to neutralize the -1 charge from chlorine. Therefore, the correct answer for the oxidation state of the unknown element X combined with chlorine in the compound XCl is +1.