In a radioactive decay process, the negatively charged emitted $$\beta $$-particles are

Two radioactive substances A and B have decay constants 5$$\lambda $$ and $$\lambda $$ respectively. At t = 0 they have the same number of nuclei. The ratio of number of nuclei of A to those of B will be (1/e)² after a time interval

The radius of germanium (Ge) nuclide is measured to be twice the radius of $${}_4^9$$Be. The number of nucleons in Ge are

Ionization potential of hydrogen atom is 13.6 eV. Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV. According to Bohr's theory, the spectral lines emited by hydrogen will be