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Complete the reaction
$n + {}_{92}^{235}U \to {}_{56}^{144}{Ba} + . . . + 3 n$

${}_{36}^{89}{Kr}$

${}_{36}^{90}{Kr}$

${}_{36}^{91}{Kr}$

${}_{36}^{92}{Kr}$

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Explanation

(a) ${}_{0}^{1}n + {}_{92}^{235}U \to {}_{56}^{144}{Ba} + {}_{36}^{89}{Kr} + 3 {}_{0}^{1}n$

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1 atomic mass unit is equal to

$\frac{1}{25}$ (mass of $F_{2}$ molecules)

$\frac{1}{14}$ (mass of $N_{2}$ molecules)

$\frac{1}{12}$ (mass of one C-atom)

$\frac{1}{16}$ (mass of $O_{2}$ molecules)

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Explanation

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The nucleus ${}_{92}^{234}U$ splits exactly in half in a fission reaction in which two neutrons are released. The resultant nuclei are

${}_{46}^{116}{Pd}$

${}_{45}^{117}{Rh}$

${}_{45}^{116}{Rh}$

${}_{46}^{117}{Pd}$

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Explanation

(a) ${}_{92}U^{234} \to {}_{46}X^{116} + {}_{46}X^{116} + (2 {OH}^{1}) {}_{46}X^{116} is {}_{46}{Pd}^{116}$

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Which of the following cannot cause fission in a heavy nucleus

$α$ -particle

Proton

Deutron

Laser rays

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Explanation

(d) Laser rays can not cause fission in heavy nucleus as they are combination of photons.

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If the mass number of an atom is A = 40 and its electron configuration is $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6}$ , the number of neutrons and protons in its nucleus will be

22, 18

18, 22

20, 20

18, 18

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Explanation

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

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Which of the following is most unstable

Electrons

Protons

Neutrons

$α$ -particle

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Explanation

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

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The nuclei of which one of the following pairs of nuclei are isotones

${}_{34}^{74}{Se}, {}_{31}^{71}{Ca}$

${}_{42}^{92}{Mo}, {}_{40}^{92}{Zr}$

${}_{38}^{81}{Sr}, {}_{38}^{86}{Sr}$

${}_{20}^{40}{Ca}, {}_{16}^{32}S$

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Explanation

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

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Fission of nuclei is possible because the binding energy per nucleon in them

Increases with mass number at high mass numbers

Decreases with mass number at high mass numbers

Increases with mass number at low mass numbers

Decreases with mass number at low mass numbers

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Explanation

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.

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Radioactive substance do not emit

Electron

Helium nucleus

Positron

Proton

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Explanation

(d)

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During a negative beta decay

An atomic electron is ejected

An electron which is already present within the nucleus is ejected

A neutron in the nucleus decays emitting an electron

A part of the binding energy is converted into electron

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Explanation

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