What is the half-life period of a nucleus in $days$ if at the end of $4.2$ $days$,$N = 0.798 \ N_0$?

The rate of radioactive disintegration at an instant for a radioactive sample of half-life $2.2 \times 10^{9} \ s$ is $10^{10} \ s^{-1}$. The number of radioactive atoms in that sample at that instant is:

$2 \text{ g}$ of a radioactive sample having a half-life of $15$ days was synthesized on $1^{st}$ Jan $2009$. The amount of the sample left behind on $1^{st}$ March $2009$ (including both the days) is: (in $\text{ g}$)

$A$ radioactive sample decays to half of its initial concentration in $6.93 \ min$. It further decays half in next $6.93 \ min$. The rate constant for the reaction is ..... $\min^{-1}$

Decay of $_{92}U^{235}$ is $...$ order reaction.

$10 \ g$ of a radioactive substance is reduced to $1.25 \ g$ after $15 \ days$. Its $1 \ kg$ mass will reduce to $500 \ g$ in how many days?