According to Bohr's theory, the electronic energy of hydrogen atom in the n^th Bohr's orbit is given by $${E_n} = {{ - 21.6 \times {{10}^{ - 19}}} \over {{n^2}}}J$$. Calculate the longest wavelength of light (in Å) that will be needed to remove an electron from the third Bohr orbit of the He⁺ ion.

Amongst the following elements (whose electronic configuration are given below), the one having the highest ionization energy is:

The shape of [CH₃]⁺ is _____.

The presence of polar bonds in a poly-atomic molecule suggests that the molecule has non-zero dipole moment.