For a reaction, $$A+2 B \rightarrow$$ Products, when concentration of $$B$$ alone is increased half-life remains the same. If concentration of $$A$$ alone is doubled, rate remains the same. The unit of rate constant for the reaction is

If the rate constant for a first order reaction is $$k$$, the time $$(t)$$ required for the completion of $$99 \%$$ of the reaction is given by

The rate of a gaseous reaction is given by the expression $$k[A][B]^2$$. If the volume of vessel is reduced to one half of the initial volume, the reaction rate as compared to original rate is

Higher order $$(>3)$$ reactions are rare due to