Given below are 4 subatomic particles travelling with the same velocity "v". Which of them will have the shortest wavelength?

$$[A]=\text { Proton }[B]=\text { Neutron. }[C]=\text { Alpha particle. }[D]=\text { Electron. }$$

The mass number of an element $$\mathrm{X}$$ is 175 with 104 neutrons in its nucleus. Into which one of the following orbitals will the last electron enter?

Bohr's radius of 2 nd orbit of $$\mathrm{Be}^{3+}$$ is equal to that of

The ion that is isoelectronic with $$\mathrm{CO}$$ is