In a first-order reaction A $$ \to $$ B, if k is rate constant and initial concentration of the reactant A is 0.5 M, then the half-life is

The reaction of hydrogen and iodine monochloride is given as :
H_2(g) + 2ICl_(g) $$ \to $$ 2HCl_(g) + I_2(g)
This reaction is of first order with respect to H_2(g) and ICl_(g),
following mechanisms were proposed.

Mechanism A :
     H_2(g) + 2ICl_(g) $$ \to $$ 2HCl_(g) + I_2(g)
Mechanism B :
     H_2(g) + ICl_(g) $$ \to $$ HCl_(g) + HI_(g) ; slow
     HI_(g) + ICl_(g) $$ \to $$ HCl_(g) + I_2(g) ; fast

Which of the above mechanism(s) can be consistent with the given information about the reaction?

Consider the reaction :  N_2(g) + 3H_2(g) $$ \to $$ 2NH_3(g)

The equality relationship between $${{d\left[ {N{H_3}} \right]} \over {dt}}$$ and $$ - {{d\left[ {{H_2}} \right]} \over {dt}}$$ is

For the reaction, 2A + B $$ \to $$ 3C + D, which of the following does not express the reaction rate?