T1/2 depends inversely on k why ?

T1/2 depends inversely on k and directly on the initial concentration of the reactants in question. What is the order?

-is the order 0 or 2nd? I think it is 0 because the [] is on top opposed to 1/[]

Radiochemical calculations of the form

ln(No/N) = kt where
k = 0.693/t1/2
are first order.