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NEET Practice Questions (MCQs) with Answers & Solutions

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Beta rays emitted by a radioactive material are

Electromagnetic radiation

The electrons orbiting around the nucleus

Charged particles emitted by nucleus

Neutral particles

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Explanation

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Alpha rays emitted from a radioactive substance are

Negatively charged particles

Ionised hydrogen nuclei

Doubly ionised helium atom

Uncharged particles having the mass equal to proton

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Explanation

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Half life of ${Bi}^{210}$ is 5 days. If we start with 50,000
atoms of this isotope, the number of atoms left over after 10
days is

5,000

25,000

12,500

20,000

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Explanation

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A nucleus of atomic mass A and atomic number Z emits $β$ -particles. The atomic mass and atomic number of the resulting nucleus are

A, Z

A + 1, Z

A, Z + 1

A-4, Z-2

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Explanation

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The radioactivity of a certain radioactive element drops to 1/64 of its initial value in 30 seconds. Its half life is

2 seconds

4 seconds

5 seconds

6 seconds

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Explanation

(c) $N = N_{0} {(\frac{1}{2})}^{t / T} \Rightarrow \frac{N_{0}}{64} = N_{0} {(\frac{1}{2})}^{30 / T} \Rightarrow T = \frac{30}{6} = 5 \sec$

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Radioactivity was discovered by

Becquerel

Pierre Curie

Roentgen

Rutherford

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Explanation

(a) Radioactivity was discovered by Becquerel .

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The average life T and the decay constant $λ$ of a radioactive nucleus are related as

$Tλ = 1$

$T = \frac{0.693}{λ}$

$\frac{T}{λ} = 1$

$T = \frac{c}{λ}$

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Explanation

(a) $Average life T = \frac{Sum of all lives of all the atom}{Total number of atoms} = \frac{1}{λ}$

$\Rightarrow Tλ = 1$

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If T is the half life of a radioactive material, then the fraction that would remain after a time $\frac{T}{2}$ is

$\frac{1}{2}$

$\frac{3}{4}$

$\frac{1}{\sqrt{2}}$

$\frac{\sqrt{2} - 1}{\sqrt{2}}$

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Explanation

$\frac{N}{N_{0}} = {(\frac{1}{2})}^{n} = {(\frac{1}{2})}^{t / T} ∴ \frac{N}{N_{0}} = {(\frac{1}{2})}^{\frac{T / 2}{T}} = {(\frac{1}{2})}^{1 / 2} = \frac{1}{\sqrt{2}}$

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If the decay or disintegration constant of a radioactive substance is $λ$ , then its half life and mean life are respectively

$\frac{1}{λ}$ and $\frac{\log_{e} 2}{λ}$

$\frac{\log_{e} 2}{λ}$ and $\frac{1}{λ}$

${λlog}_{e} 2$ and $\frac{1}{λ}$

$\frac{λ}{\log_{e} 2}$ and $\frac{1}{λ}$

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Explanation

(b) $H a l f l i f e = \frac{\log 2}{λ} M e a n l i f e = \frac{1}{λ}$

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Which of the following is in the increasing order for penetrating power

$α, β, γ$

$β, α, γ$

$γ, α, β$

$γ, β, α$

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Explanation

(a) Penetration power of $γ$ is 100 times of $β$ , while that of $β$ is 100 times of $α$ .

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