The order of a reaction `underline("can be")` calculated from law of mass action.

Explanation

To solve the question regarding the order of a reaction and its relation to the law of mass action, we can break it down into the following steps:

### Step 1: Understand the Law of Mass Action
The law of mass action states that the rate of a chemical reaction is proportional to the product of the concentrations of the reactants, each raised to a power corresponding to their stoichiometric coefficients in the balanced equation. For a reversible reaction \( A \rightleftharpoons B \), the rates can be expressed as:
- Rate of the forward reaction: \( \text{Rate}_{\text{forward}} = k_f [A]^{n} \)
- Rate of the backward reaction: \( \text{Rate}_{\text{backward}} = k_b [B]^{m} \)

### Step 2: Define Reaction Order
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