does the half life formula t=ln2/k give sec as unit or min as unit
It depends upon what the half life is measured in. If the half life is 3.54 sec then k is in sec^-1. If half life is 4.5 min, then k is in min^-1. You may be asking the other way around (what unit for half life if k .....) but I think you gt the idea.
The formula for half-life, t = ln(2)/k, gives the half-life time in terms of the unit of k, which represents the rate constant of the decay process. The unit of k depends on the specific reaction or process being considered.
If k is given in units of per second (s^(-1)), then the half-life time, t, resulting from the formula will be in seconds (s). Similarly, if k is given in units of per minute (min^(-1)), then the half-life time, t, will be in minutes (min).
To determine the unit of time (sec or min) for the half-life result, you need to determine the unit of the rate constant (k) associated with the specific decay process or reaction you are considering.