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1

### AIPMT 2009

Which of the following is not permissible arrangement of electrons in an atom ?
A
n = 5, $$l$$ = 3, m = 0, s = +1/2
B
n = 3, $$l$$ = 2, m = $$-$$ 3, s = $$-$$1/2
C
n = 3, $$l$$ = 2, m = $$-$$ 2, s = $$-$$1/2
D
n = 4, $$l$$ = 0, m = 0, s = $$-$$1/2

## Explanation

In an atom for any value of n, the values of l = 0 to (n-1)

For a given value of l, the values of ml = -$$l$$ to 0 to +$$l$$

and the value of s = +1/2 or -1/2

In option(b), l = 2 and ml = -3

This is not possible. as for l = 2 min value of ml = -2
2

### AIPMT 2009

Maximum number of electrons in a subshell of an atom is determined by the following
A
2$$l$$ + 1
B
4$$l$$ $$-$$ 2
C
2n2
D
4$$l$$ + 2

## Explanation

Maximum number of electrons in a subshell = 2(2l+1) = 4l + 2
3

### AIPMT 2008

If uncertainty in position and momentum are equal, then uncertainty in velocity is
A
$${1 \over m}\sqrt {{h \over \pi }}$$
B
$$\sqrt {{h \over \pi }}$$
C
$${1 \over {2m}}\sqrt {{h \over \pi }}$$
D
$$\sqrt {{h \over {2\pi }}}$$

## Explanation

According to Heisenberg uncertainty principle

$$\Delta p.\Delta x \ge {h \over {4\pi }}$$ or m$$\Delta v.\Delta x \ge {h \over {4\pi }}$$

$$\Rightarrow$$ (m$$\Delta v$$)2 $$\ge {h \over {4\pi }}$$ ($$\because$$ $$\Delta x$$ = $$\Delta p$$)

$$\Rightarrow$$ $$\Delta v \ge$$ $${1 \over {2m}}\sqrt {{h \over \pi }}$$
4

### AIPMT 2008

The measurement of the electron position is associated with an uncertainty in momentum, which is equal to 1 $$\times$$ 10$$-$$18 g cm s$$-$$1. The uncertainty in electron velocity is (mass of an electron is 9 $$\times$$ 10$$-$$28 g)
A
1 $$\times$$ 105 cm s$$-$$1
B
1 $$\times$$ 1011 cm s$$-$$1
C
1 $$\times$$ 109 cm s$$-$$1
D
1 $$\times$$ 106 cm s$$-$$1

## Explanation

$$\Delta v$$ = $${{1 \times {{10}^{ - 18}}} \over {9 \times {{10}^{ - 28}}}} = 1.1 \times {10^9}cm\,{s^{ - 1}}$$

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NEET

Class 12