How many unit cells are present in $39 \ g$ of potassium that crystallises in body-centred cubic structure? [At. wt. of $K = 39$]

If the population grows at the rate of $8 \%$ per year,then the time taken for the population to be doubled is (Given $\log 2=0.6912$ ) (in $\text{ years}$)

When electromagnetic radiation of wavelength $300 \ nm$ falls on the surface of a metal,electrons are emitted with the kinetic energy of $1.68 \times 10^5 \ J \ mol^{-1}$. What is the minimum energy needed to remove an electron from the metal? $(h = 6.626 \times 10^{-34} \ J \ s, c = 3 \times 10^8 \ m \ s^{-1}, N_A = 6.022 \times 10^{23} \ mol^{-1})$

An electronic transition in a hydrogen atom results in the formation of the $H_\alpha$ line of the hydrogen spectrum in the Lyman series. The energies associated with the electron in each of the orbits involved in the transition (in $kcal \ mol^{-1}$) are:

What is the objective of Systematics?

If $p \Rightarrow (q \vee r)$ is false,then the truth values of $p, q, r$ are respectively