What is the unit for the zero order rate constant?

In the reaction,$A \rightarrow$ products,if the concentration of the reactant is doubled,the rate of the reaction remains unchanged. The order of the reaction with respect to $A$ is

$A \rightarrow B$
The above reaction is of zero order. The half-life of this reaction is $50 \ min$. The time taken for the concentration of $A$ to reduce to one-fourth of its initial value is $........... \ min$ (Nearest integer).

The reaction $A \to \text{Products}$ is a zero-order reaction. If the initial concentration of $A$ is $2 \ M$,then at time $t = 1/K$ (where $K$ is the rate constant),the concentration of $A$ will be ......... $M$.

The decomposition of $NH_3$ on the platinum surface is a zero-order reaction. If $K = 2.5 \times 10^{-4} \ mol \ L^{-1} \ s^{-1}$,what will be the rate of production of $H_2$ in $mol \ L^{-1} \ s^{-1}$ unit?

The rate equation for a reaction $A \rightarrow B$ is $r=k[A]^{0}$. If the initial concentration of the reactant is $a \ mol \ dm^{-3}$,the half-life period of the reaction is