### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2002

MCQ (Single Correct Answer)
If ${N_0}$ is the original mass of the substance of half-life period ${t_{1/2}} = 5$ years, then the amount of substance left after $15$ years is
A
${N_0}/8$
B
${N_0}/16$
C
${N_0}/2$
D
${N_0}/4$

## Explanation

After every half-life, the mass of the substance reduces to half its initial value.

${N_0}\mathop \to \limits^{5\,years} \,\,{{{N_0}} \over 2}\mathop \to \limits^{5\,years} {{{N_0}} \over {{2^2}}}\mathop \to \limits^{5\,years} {{{N_0}} \over 8}$
2

### AIEEE 2002

MCQ (Single Correct Answer)
At a specific instant emission of radioactive compound is deflected in a magnetic field. The compound can emit
\eqalign{ & \left( i \right)\,\,\,\,\,\,\,electrons\,\,\,\,\,\,\,\,\,\,\,\,\left( {ii} \right)\,\,\,\,\,\,\,protons \cr & \left( {iii} \right)\,\,\,H{e^{2 + }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {iv} \right)\,\,\,\,\,\,\,neutrons \cr}

The emission at instant can be

A
$i, ii, iii$
B
$i, ii, iii, iv$
C
$iv$
D
$ii, iii$

## Explanation

Charged particles are deflected in magnetic field.
3

### AIEEE 2002

MCQ (Single Correct Answer)
If $13.6$ $eV$ energy is required to ionize the hydrogen atom, then the energy required to remove an electron from $n=2$ is
A
$10.2$ $eV$
B
$0$ $eV$
C
$3.4$ $eV$
D
$6.8$ $eV.$

## Explanation

KEY CONCEPT :

The energy of nth orbit of hydrogen is given by

${E_n} = {{13.6} \over {{n^2}}}eV/$ atom

For $n=2,$ ${E_n} = {{ - 13.6} \over 4} = - 3.4eV$

Therefore the energy required to remove electron from

$n = 2$ is $+3.4eV.$

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