Q. **Select the correct statements.**

a) An electron is in orbit,can absorb only one photon and that too equivalent in energy to the energy difference between two orbits.

b) 3d subshell penetrates more towards nucleus than 4s.

c) Green light is never emitted in black body radiations.

d) The energy change between two successive orbitals increases with increasing value of n.

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a) When an electron is in orbit, it can absorb only one photon and that too equivalent in energy to the energy difference between two orbits, i.e. `DeltaE = hnu`

This follows from Bohr’s postulates of stationary orbits of atoms. So, option A) is correct

b) 4s orbital is more penetrating towards the nucleus than 3d orbitals and that is the reason, 4s orbitals are filled up before 3d as exemplified in potassium (19) atom which has the electron configuration `1s^2 2s^2 2p^6 3s^2 3p^6 4s^1` rather than `1s^2 2s^2 2p^6 3s^2 3p^6 3d^1` . Hence option B) is wrong.

c) Black body radiation contains all of the wavelengths, including those of the green ight. The reason that it doesn't look green is that the longer wavelength light, like infrared and red, overwhelm the amount of green light. Option C) is wrong again.

The energy difference between two successive orbits can be obtained from the Rydberg formula

`DeltaE = R_oo(1/n_2^2-1/n_1^2)`

With increasing value of `n_i` , this difference also increases. Option D) is correct.

**Therefore correct statements are at options A) and D).**

**Sources:**

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