(A). The order of a reaction is an experimental quantity: Unlike molecularity, which can be determined by looking at a balanced chemical equation for an elementary step, the order of a reaction can only be determined through experimental data.

(B). Order can be zero: A zero-order reaction occurs when the rate of the reaction is independent of the concentration of the reactants. You can see this in the half-life formula $t_{0.5} = \frac{[R]_0}{2k}$, where the rate constant $k$ is independent of concentration.

(C). Order can be fractional value: While molecularity must be a whole number, the reaction order (derived experimentally) can be a fraction (e.g., $1.5$ or $0.5$) depending on the complex mechanism of the reaction.

(D). Order is applicable to elementary as well as complex reactions: Molecularity is only meaningful for elementary (single-step) reactions. However, "order" is a term used to describe the overall rate law for both simple single-step reactions and complex multi-step reactions.