Which from following equations is used to express the angular momentum of an electron in a stationary state?

Which emission transition series is obtained when electron jumps from $$\mathrm{n}_2=\infty$$ to $$\mathrm{n}_1=1$$ ?

What is half life time of a first order reaction if initial conc. of reactant is $$0.01 \mathrm{~mol} \mathrm{~L}^{-1}$$ and rate of reaction is $$0.00352 \mathrm{~mol} \mathrm{~L}^{-1}$$ minute $$^{-1}$$ ?

Which among the following pairs of polymers contains both members as copolymers?