CBSE
Multiple Choice QuestionsThe half - life of a radioactive isotope X is 50 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1: 15 in a sample of a given rock. The age of the rock was estimated to be
200 yr
250 yr
100 yr
100 yr
Fusion reaction takes place at high temperature because
atoms get ionised at high temperature
kinetic energy is high enough to overcome the coulomb repulsion between nuclei
molecules break up at high temperature
molecules break up at high temperature
A nucleus 
emits one α - particle and two β- particles. The resulting nucleus is
A nucleus of uranium decays at rest into nuclei of thorium and helium. Then,
the helium nucleus has more kinetic energy than the thorium nucleus
the helium nucleus has less momentum than the thorium nucleus
the helium nucleus has more momentum than the thorium nucleus
the helium nucleus has more momentum than the thorium nucleus
Two radioactive nuclei P and Q, in a given sample decay into a stable nucleous R. At time t =0, number of P species are 4No and that of Q are No.Half -life of P (for conversion to R) is 1 min where asthat of Q is 12 min. Initially there are no nuclei of R present in the sample. When number of nuclei of R presnent in the sample would be
3No
9No / 2
5No/2
5No/2
The mass of a 
nucleus is 0.042u less than the sum of the masses of all its nucleons. The binding energy per nucleon is 
nucleus is nearly
46 MeV
5.6 MeV
3.9 MeV
3.9 MeV
The activity of a radioactive sample is measured as No counts per minute at t = 0 and No/e counts per minute at t = 5 min. The time (in minute) at which the activity reduces to half its value is
loge 2 /5
5/ loge 2
5 log10 2
5 log10 2
The decay constant of a ratio isotope is λ. If A1 and A2 are its activities at times t1 and t2 respectively, te number of nuclei which have decayed during the time (t1-t2)
A1t1 - A2t2
A1 - A2
(A1 - A2)/λ
(A1 - A2)/λ
The binding energy per nucleon in deuterium and helium nuclei are 1.1 MeV and 7.0 MeV, respectively. When two deuterium nuclei fuse to form a helium nucleus the energy released in the fusion is
23.6 MeV
2.2 MeV
28.0 MeV
28.0 MeV
In the nuclear decay given below,
the particle emitted in the sequence are
β, α, γ
γ, β, α,
β,γ, α
β,γ, α
