## If the radius of 2nd Bohr orbit of hydrogen atom is r2. The radius of third Bohr orbit will be

Problem : If the radius of 2nd Bohr orbit of hydrogen atom is r2. The radius of third Bohr orbit will be

(A) $\large \frac{4}{9}r_2$

(B) $\large 4 r_2$

(C) $\large \frac{9}{4}r_2$

(D) $\large 9 r_2$

Ans: (C)

Sol: $\large r_n = \frac{n^2 h^2}{4\pi^2 m K Z e^2}$

$\large r_n \propto n^2$

$\large \frac{r_2}{r_3} = \frac{2^2}{3^2}$

$\large r_3 = \frac{9}{4}r_2$

## Principal. Azimuthal and magnetic quantum numbers are respectively related to

Problem : Principal. Azimuthal and magnetic quantum numbers are respectively related to

(A) Size , orientation and shape

(B) Size , shape and orientation

(C) Shape , size and orientation

(D) None of these

Solution: Principal gives size, azimuthal gives shape and magnetic quantum number gives the orientation

Ans: (B)

## What transition in the hydrogen spectrum would have the same wavelength…

Problem : What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition, n = 4 to n = 2 in the He+ spectrum.

(A) n = 4 to n = 2

(B) n = 3 to n = 2

(C) n = 3 to n = 1

(D) n = 2 to n = 1

Ans: (D)

Solution: $\large \frac{1}{\lambda} = (\frac{1}{2^2} – \frac{1}{4^2}) = \frac{3}{4}R$

In H-spectrum for the same λ as Z = 1, n1 = 1, n2 = 2

## If an electron in H-atom has an energy of – 78.4 kcal/mol…

Problem : If an electron in H-atom has an energy of – 78.4 kcal/mol. The orbit in which the electron is present is:

(A) 1st

(B) 2nd

(C) 3rd

(D) 4th

Ans: (B)

Solution: $\large E_n = -\frac{313.6}{n^2} kcal/mol$

$\large – 78.4 = -\frac{313.6}{n^2}$

n = 2

## Which of the following pairs of ions have the same electronic configuration ?

Problem : Which of the following pairs of ions have the same electronic configuration ?

(A) Cr3+, Fe3+

(B) Fe3+, Mn2+

(C) Fe3+, Co3+

(D) Se3+, Cr3+

Solution: Fe3+ and Mn2+ have same electronic configuration
Ans: (B)