NEET Practice Questions (MCQs) with Answers & Solutions

(a) Number of protons = 2 + 2 + 6 + 2 + 6 = 18
Number of neutrons = 40 – 18 = 22.

(c) Neutrons are unstable and having mean life time of 32 sec, decaying by emitting an electron and antineutrino to become proton.

(a) These nuclei having different Z and A but equal (A – Z) are called isotones.

Fission of heavy nuclei is possible because the binding energy per nucleon decreases with increasing mass number at high mass numbers. This makes the heavier nuclei less stable, and they can undergo fission to release energy and form more stable nuclei with higher binding energy per nucleon.

(d)

(c) Negative $\mathrm{\beta }$-decay is expressed by the equation $\mathrm{n}={\mathrm{p}}^{+}+{\mathrm{e}}^{-}+{\mathrm{v}}^{-}$

(a) No radioactive substance emit both $\mathrm{\alpha }$ and $\mathrm{\beta }$ particles simultaneously. Some substances emit $\mathrm{\alpha }$-particles and some other emits $\mathrm{\beta }$-particles. $\mathrm{\gamma }$ rays are emitted along with both and particles.

(c) $\mathrm{\gamma }$-rays are highly penetrating.

(c) Average life $\frac{1}{\mathrm{\lambda }}=\frac{1600}{0.693}=2308\approx 2319$years.

(d) Fraction of atoms remains after five half lives
$\frac{\mathrm{N}}{{\mathrm{N}}_0}={\left(\frac{1}{2}\right)}^{\mathrm{t}/\mathrm{T}}={\left(\frac{{\displaystyle 1}}{{\displaystyle 2}}\right)}^{5\mathrm{T}/\mathrm{T}}=\frac{1}{32}$
$\Rightarrow$Percentage atom remains = $\frac{1}{32}\times 100=3.125\%$