The kinetic energy of an electron in the second Bohr orbit of a hydrogen atom is [$$\alpha_0$$ is Bohr radius]

An organic compound undergoes first-order decomposition. The time taken for its decomposition to 1/8 and 1/10 of its initial concentration are t_1/8 and t_1/10 respectively. What is the value of $$\left[ {{{{t_{1/8}}} \over {{t_{1/10}}}}} \right] \times 10$$? ($${\log _{10}}2 = 0.3$$)

The periodic table consists of 18 groups. An isotope of copper, on bombardment with protons undergoes a nuclear reaction yielding element X as shown below. To which group, element X belongs in the periodic table?

$${}_{29}^{63}Cu$$ + $${}_1^1H$$ $$\to$$ $$6{}_0^1n$$ + $${}_2^4\alpha $$ + 2$${}_1^1H$$ + X

29.2 % (w/w) HCl stock solution has density of 1.25 g mL^-1 . The molecular weight of HCl is 36.5 g mol^-1 . The volume (mL) of stock solution required to prepare a 200 mL solution of 0.4 M HCl is