1

### IIT-JEE 1981

Subjective
The energy of the electron in the second and the third Bohr's orbits of the hydrogen atom is -5.42 $\times$ 10-12 erg and -2.41 $\times$ 10-12 erg respectively. Calculate the wavelength of the emitted radiation when the electron drops from the third to second orbit.

## Answer

6.603 Å
2

### IIT-JEE 1978

Subjective
Naturally occurring boron consists of two isotopes whose atomic weighs are 10.01 and 11.01. The atomic weight of natural oron is 10.81. Calculate the percentage of each isotope in natural boron.

## Answer

80%

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