The order of reaction must be determined experimentally or by calculation.
The order of reaction is the power to which a reactant must be raised in the rate law of the reaction. The rate law must be determined experimentally or by calculation. It can not just be deduced from the reaction equation.
In this case, the question is incomplete hence we can not deduce the order of reaction with respect to HCl. However, this order of reaction can be obtained by calculation.
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