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1.

Uranium (`""_(92)U""^(238)`) decayed to `""_(82)Pb""^(206)`. The process is `""_(92)U""^(238)underset(xalpha,ybeta)to.""_(82)Pb""^(206)` `t""_(1//2)of U""^(238)=4.5xx10""^(9)` years x and y in above decay series areA. 6.8B. 9.6C. 8.8D. 8.6

Answer» Correct Answer - d
`alpha=(Ap-Ad)/4,beta=2xxalpha-(Zp-Zd)`
Discussion
2.

Uranium (`""_(92)U""^(238)`) decayed to `""_(82)Pb""^(206)`. The process is `""_(92)U""^(238)underset(xalpha,ybeta)to.""_(82)Pb""^(206)` `t""_(1//2)of U""^(238)=4.5xx10""^(9)` years The analysis of a rock shows the relative number of `U""^(238)` and `Pb""^(206)` atoms (Pb/U=0.25). The age of rock will beA. `2.303/0.693xx4.5xx10""^(9)log1.25`B. `2.303/0.693xx4.5xx10""^(9)log0.25`C. `2.303/0.693xx4.5xx10""^(9)log4`D. `2.303/(4.5xx10""^(9))xx0.693log4`

Answer» Correct Answer - a
Discussion
3.

Uranium (`""_(92)U""^(238)`) decayed to `""_(82)Pb""^(206)`. The process is `""_(92)U""^(238)underset(xalpha,ybeta)to.""_(82)Pb""^(206)` `t""_(1//2)of U""^(238)=4.5xx10""^(9)` years A sample of rock from South America contains equal number of atoms of `U""^(238)` and `Pb""^(""^(206)`. The age of the rock will beA. `4.5xx10""^(9)years`B. ?C. `13.5xx10""^(9)years`D. `2.25xx10""^(9)years`

Answer» Correct Answer - a
`t=2.303/0.693t""_(1//2)log.(1+(pb""^(206))/U""^(238))`
Discussion
4.

Uranium `._(92)U^(238)` decayed to `._(82)Pb^(206)`. They decay process is `._(92)U^(238) underset((x alpha, y beta))(rarr ._(82)Pb^(206))` `t_(1//2)` of `U^(238) = 4.5 xx 10^(9)` years A sample of rock south America contains equal number of atoms of `U^(238)` and `Pb^(206)`. The age of rock will beA. `4.5 xx 10^(9)` yearsB. `9 xx 10^(9)` yearsC. `13.5 xx 10^(9)` yearsD. `2.25 xx 10^(9)` years

Answer» Correct Answer - A
`K = (2.303)/(t) "log" ((N_(0))/(N))`
`(0.693)/(t_(1//2)) = (2.303)/(t) "log" ((N_(0))/(N))` `[{:(N_(0) = 1 + 1 = 2),(N = 1):}]`
`(0.693)/(4.5 xx 10^(9)) = (2.303)/(t) "log" ((2)/(1))`
`:.t = 4.5 xx 10^(9)` years
Discussion
5.

In the nuclear reaction `._(92)U^(238) rarr ._(82)Pb^(206)`, the number of alpha and beta particles decayed areA. `4 alpha, 3 beta`B. `8 alpha, 6 beta`C. `6 alpha, 4 beta`D. `7 alpha, 5 beta`

Answer» Correct Answer - B
Number of `alpha`- particles `= (238 - 206)/(4) = 8`
Number of `beta`- particles `= 2xx 8 - 92 + 82 = 6`
Discussion
6.

Uranium `._(92)U^(238)` decayed to `._(82)Pb^(206)`. They decay process is `._(92)U^(238) underset((x alpha, y beta))(rarr ._(82)Pb^(206))` `t_(1//2)` of `U^(238) = 4.5 xx 10^(9)` years Atomic mass of `U^(238)` is 238.125 amu. Its packing fraction will beA. 6.25B. 0.125C. 12.5D. 5.25

Answer» Correct Answer - d
`t=(2.303xxt""_(1//2))/0.693log.(1+(pb""^(206))/U""^(238))`
Discussion
7.

The half of `""_(92)""^(238)U` against `alpha`-decay is `4.5xx10""^(9)`year. The time taken in year for the decay of `15/16` part of the isotope isA. `9.0xx10""^(9)`B. `1.8xx10""^(10)`C. `4.5xx10""^(9)`D. `2.7xx10""^(10)`

Answer» Correct Answer - b
`N=N""_(0)/2""^(n)(n=t//t""_(1//2))`
Discussion
8.

The total number of `alpha and beta` particles emitted in the nuclear reaction `._(92)^(238)U rarr ._(82)^(214)Pb` is

Answer» Correct Answer - 8
`._(92)^(238)U rarr ._(82)^(214)Pb + 6(._(2)^(4)He) + 2 (._(-1)e^(0))`
`alpha = 6, beta = 2`
Total = 8
Discussion
9.

A closed vessel with rigid walls contains 1 mol of `._(92)^(238)U` and 1 mole of air at 298K. Considering complete decay of `._(92)^(238)U " to " ._(82)^(206)Pb`, the ratio of the final pressure to the initial pressure of the system at 298 K is

Answer» Correct Answer - 9
Initial moles of gases = 1
`underset("Initial moles 1 mole")(._(92)^(238)U rarr ._(82)^(206)Pb) + underset(8 "mole")(8_(2)^(4) He + 6 ._(-1)e^(0))`
Moles after
Total gaseous moles after decomposition `= 8 + 1 = 9` moles
Ratio of pressures `(P_(f))/(P_(i)) = (n_(f))/(n_(i)) = 9`
Discussion
10.

There are four radioactive decay series called thorium `(4n)`, uranium `(4n + 2)` actinium `(4n + 3)` and neptunium `(4n + 1)` series. Neptunium series is artificial while other three series are natural. The end productsd of each radioacitve decay series have stable nuclei. All natural decay series terminate at lead but neptunium or artificial series terminate at bismuth. Actinium series begins with an isotope ofA. ActiniumB. RadiumC. UraniumD. Polonium

Answer» Correct Answer - C
Discussion
11.

The number of neutrons accompanyng the formation of `_(54)^(139)Xe` and `_(38)^(139)Xe` from the absorption of a slow neutron by `_(92)^(235)U` followed by nuclear fision is:

Answer» Correct Answer - 3
since the charge in mass is only due to the emmission of `alpha`-particle, we have
Number of `alpha`-particle emitted `=(234-206)/(4)=7`
Now the associated decrease in atomic number would be `14 (=2xx7)` and thus the atomic number of the daughter atom would be `76(=90-14)`. But the actual atomic number of lead is `82 e`. the atomic number is six more than expected. This is because of the emission `beta`-particle. Since there is an increase of one in atomic number due to the emission of one `beta`-particle, we have
Number of `beta`-particles emitted `=(82-76)/(1)=6`
Hence, number of `alpha`-particles emitted `=7` ltbr,. Number of `beta`-particles emittes `=6`
Answer is `6+7=13`
Discussion
12.

The number of neutrons accompanying the formation of `""_(54)""^(139)Xe and ""_(38)""^(94)Sr` from th absorption of slow neutron by `""_(92)""^(235)U`, followed by nuclear fission is

Answer» Correct Answer - d
`""_(238)""^(92)Uto""_(0)""^(1)nto""_(54)""^(139)Xe+""_(38)""^(94)Sr+3""_(0)""^(1)n`
Discussion
13.

The periodic table consists of 18 groups. An isotope of copper, on bombardment with protons, undergoes a nuclear reaction yielding element X as shown below. To which group, element X belongs in the periodic table `._(29)^(63)Cu + ._(1)^(1)H rarr 6 ._(0)^(1)n + alpha + 2 ._(1)^(1)H + X`

Answer» Correct Answer - 8
`._(29)^(63)Cu + ._(1)^(1)H rarr 6 ._(0)^(1)n + ._(2)^(1) alpha + 2 ._(1)^(1) H + X`
`64 = 6 + 4 + 2 + A rArr A = 52`
`29 + 1 = 30 = 0 + 2 + 2 + z rArr z = 26`
element X should be iron in group 8
Discussion
14.

The periosic table consists of 18 groups. An isotope of copper, on bombardment with protons, undergoes a nuclear reaction reaction yielding eklement X as shown as below. To which group, element X belongs in the periodic table? `""_(29)""^(63)Cu+""_(1)""^(1)Hto6""_(0)""^(1)n+alpha+2""_(1)""^(1)H+X`

Answer» Correct Answer - 8
group displacement law
Discussion
15.

Which of the following isotopes of uranium is most radioactive ?A. 238B. 235C. 226D. 248

Answer» Correct Answer - B
`._(92)U^(235)` is readioactive because it is most unstable
Discussion
16.

In the given reaction `._(92)U^(235) overset(-alpha)rarr (A) overset(-beta)rarr (B) overset(-beta)rarr (C)` isotopes areA. A and CB. `._(92)U^(235)` and CC. A and BD. A, B and C

Answer» Correct Answer - B
`._(92)U^(235) overset(-alpha)rarr (A) overset(-beta)rarr (B) overset(-beta)rarr (C)`
(i) `._(92 -2)A^(235-4) = ._(90)A^(231)`
(ii) `._(90)A^(231) overset(-beta)rarr ._((90 +1))B^((231)) = ._(91)B^(231)`
(iii) `._(91)B^(231) overset(-beta)rarr ._((91 +1))C^(231) = ._(92)C^(231)`
Isotopes are `._(92)U^(235) and C`
Discussion
17.

Uranium `._(92)U^(235)` on bombardment with slow neutrons producesA. DeutronsB. Fusion reactionC. Fission reactionD. Endothermic reaction

Answer» Correct Answer - C
`._(92)U^(235) + ._(0)n^(1) rarr ._(56)Ba^(145) + ._(36)Kr^(88) + 3 ._(0)^(1)n`
Discussion
18.

The periodic table consists of 18 groups. An isotope of copper, on bombardment with protons, undergoes a nuclear reaction yielding element `X` as shown below. To which group, element `X` belongs in the periodic table ? `._(29)Cu^(63)+._(1)H^(1)rarr6._(0)n^(1)+._(2)He^(4)(alpha)+2._(1)H^(1)+._(Z)X^(A)`

Answer» Correct Answer - 8
Discussion
19.

Assertion U-235 is unstable isotope of uranium. Unergo `alpha-`decay. Reason `alpha-`decay is observed with all radioactive isotopes having atomic number greater than 82.A. Both Assertion and Reason are correct and Reason is the correct explanation of the AssertionB. Both Assertion and Reason are correct but Reason is not the correct explanation of AssertionC. Assertion is correct but Reason is incorrectD. Assertion is incorrect but Reason is correct

Answer» Correct Answer - A
Discussion
20.

An isotope of oxygen has mass number 18. Other isotopes of oxygen will have the sameA. Mass numberB. Atomic weightC. Number of neutronsD. Number of protons

Answer» Correct Answer - D
Isotopes differ in number of neutrons but have same number of protons.
Discussion
21.

An ordinary oxygen containsA. Only `O - 16` isotopesB. Only `O - 17` isotopesC. A mixture of `O - 16 and O - 18` isotopesD. A mixture of `O - 16, O = 17 and O - 18` isotpes

Answer» Correct Answer - D
An ordinary oxygen contains a mixture of `O - 16` (99.8%), `O - 17` (0.0037%), `O - 18 (0.204%)` isotopes
Discussion
22.

The half-life of `._(6)C^(14)`, if its decay constant is `6.31 xx 10^(-4)` isA. 1098 yrB. `109.8 yr`C. `10.98 yr`D. `1.098 yr`

Answer» Correct Answer - A
`t_(1//2) = (0.693)/(k) = (0.693)/(6.31 xx 10^(-4)) = 0.1098 xx 10^(4) = 1098 yr`
Discussion
23.

`._(92)U^(235) + n rarr` fission product + neutron `+ 3.20 xx 10^(-11) J`. The energy released when 1g of `._(92)U^(235)` undergoes fission isA. `12.75 xx 10^(8) kJ`B. `18.60 xx 10^(9) kJ`C. `8.21 xx 10^(7) kJ`D. `6.55 xx 10^(6) kJ`

Answer» Correct Answer - C
`1g U-235 = (6.023 xx 10^(23))/(235)` atoms
`:.` Energy released `= 3.2 xx 10^(-11) xx (6.023 xx 10^(23))/(235) J`
`= 8.21 xx 10^(1) J = 8.2 xx 10^(7) kJ`
Discussion
24.

An example of nuclear fusion reaction isA. `._(90)Th^(233) + ._(0)n^(1) rarr ._(90)Th^(234)`B. `._(13)Al^(27) + ._(2)He^(4) rarr ._(15)p^(30) + ._(0)n^(1)`C. `._(2)He^(3) + ._(2)He^(3) rarr H_(2)He^(4) + 2 ._(1)H^(1)`D. `._(92)U^(239) rarr ._(93)Np^(239) + ._(0)e^(1)`

Answer» Correct Answer - C
Discussion
25.

The huge amount of energy which is released during atomic fission is due toA. Loss of massB. Loss of electronsC. Loss of protonsD. Loss of `alpha`-particles

Answer» Correct Answer - A
The huge amount of energy released during atomic fission is due to loss of mass.
Discussion
26.

From the following equations pick out the possible nuclear fusion reaction:A. `""_(6)""^(13)C+""_(1)""^(1)Hto""_(6)""^(14)C+""_(1)""^(0)e+4.3MeV`B. `""_(6)""^(12)C+""_(1)""^(1)Heto""_(7)""^(13)N+2MeV`C. `""_(7)""^(14)C+""_(1)""^(1)Heto""_(8)""^(15)O+7.3MeV`D. `""_(92)""^(235)U+""_(0)""^(1)nto""_(54)""^(140)Xe+""_(38)""^(94)Sr+""_(0)""^(1)n+gamma+200MeV`

Answer» Correct Answer - b,c
Discussion
27.

The numberr of neutrons emitted when `""_(92)""^(235)U` undergoes controlled nuclear fission to `""_(54)""^(142)Xe` and `""_(38)""^(90)Sr` isA. 2B. 3C. 5D. 0

Answer» Correct Answer - b
`""_(235)""^(92)Uto""_(54)""^(142)Xe+""_(38)""^(90)Sr+3""_(0)""^(1)n`
Discussion
28.

Calculate the number of neutrons emitted when `._(92)U^(235)` undergoes controlled nuclear fission to `._(54)Xe^(142) ` and `._(38)Sr^(90)`.

Answer» `._(92)U^(235)rarr._(54)Xe^(142)+._(38)Sr^(90)=x._(0)n^(1)`
Equating atomic number on both sides
`235=142+90+x` ltbr. `:. X=3`
Hence, 3 neutrons are emitted.
Discussion
29.

Why a huge amount of energy is released in nuclear fission of nuclear fusion solution.

Answer» This is because of a large mass defect, i.e., `E = Delta mc^(2)`, where `Delta m =` mass defect and `c =` velocity of light.
Discussion
30.

The percentage efficiency of nuclear fissiion is higher than nuclear fusion.

Answer» Correct Answer - F
Discussion
31.

Statement 1 : Hydrogen bomb involves not only fusion but also fission reactions to start the fusion whereas atom bomb involves only fission. Statement 2 : Though energy liberated per fusion is smaller than energy liberated per fission, yet hydrogen bomb is more powerful than atom bomb.A. Statement 1 is true, statement 2 is true , statement 2 is a correct explanation for statement 2B. Statement 1 is true, Statement 2 is true, statement 2 is not a correct explanation for statement 2C. Statement 1 is true, statement 2 is falseD. Statement 1 is false, statement 2 is true

Answer» Correct Answer - B
Masses per atom of deuterium and tritium are much smaller than that of uranium.
Discussion
32.

Which of the following is an example of nuclear fissionA. `._(1)H^(2) + ._(1)H^(2) rarr ._(2)He^(4) + gamma`B. A + B `rarr C +` energyC. `._(92)U^(235) + ._(0)n^(1) rarr ._(56)Ba^(141) + ._(36)Ke^(92) + 3 ._(0)n^(1) +` energyD. `._(13)Al^(27) + ._(2)He^(4) rarr ._(15)P^(30) + ._(0)n^(1)`

Answer» Correct Answer - C
Discussion
33.

Efficiency of nuclear fusion as compared to nuclear fission is a. More b. Less c. Same d. None is correctA. a. MoreB. b. LessC. c. SameD. d. None is correct

Answer» Correct Answer - a. More
In nuclear fusion more energy is released with per gram of fuel.
Discussion