1

### AIPMT 2002

In hydrogen atom, energy of first excited state is $-$ 3.4 eV. Then find out K.E. of same orbit of hydrogen atom
A
+3.4 eV
B
+6.8 eV
C
$-$ 13.6 eV
D
+13.6 eV

## Explanation

K.E = 1/2 mv2

= ${\left( {{{\pi {e^2}} \over {nh}}} \right)^2} \times 2m$ [ $\because$ v = ${{2\pi {e^2}} \over {nh}}$]

$\therefore$ Total energy = En = ${{ - 2{\pi ^2}m{e^4}} \over {{n^2}{h^2}}}$

= -${\left( {{{\pi {e^2}} \over {nh}}} \right)^2}$ $\times$ 2m = -K.E

$\therefore$ K.E = - En

Energy of first excited state is -3.4 eV

$\therefore$ Kinetic energy of the same orbit (n = 2) will be +3.4 ev
2

### AIPMT 2001

The following quantum numbers are possible for how many orbitals :

n = 3, $l$ = 2, m = +2 ?
A
1
B
2
C
3
D
4

## Explanation

n = 3, l = 2, m = +2

It shows one of the five d-orbitals(3d)
3

### AIPMT 2001

Main axis of a diatomic molecule is z, molecular orbital px and py overlap to from which of the following orbitals.
A
$\pi$ molecular orbital
B
$\sigma$ molecular orbital
C
$\delta$ molecular orbital
D
No bond will form

## Explanation

For $\pi$ overlap, the lobes of the atomic orbitals are perpendicularto the line joining the nuclei.

Hence only sidewise overlapping takes place.
4

### AIPMT 2000

Isoelectronic species are
A
CO, CN$-$, NO+, C${_2^{2 - }}$
B
CO$-$, CN, NO,
C
$C_2^ -$
D
CO, CN, NO, C2

## Explanation

No. of electrons CO = CN- = NO+ = $C_2^{2 - }$ = 14, So these are isoelectronics.