A sample of radioactive element has a mass of 10 g at an instant t = 0. The approximate mass of this element in the sample after two mean lives is [2003]

1. 3.70 g

2. 6.30 g

3. 1.35 g

4. 2.50 g

The mass density of a nucleus varies with mass number A as 

1. $A^2$

2. A 

3. Constant 

4. $\frac{1}{A}$

A nuclear decay is expressed as:
\(_{6}^{11}\mathrm{C}\rightarrow _{5}^{11}\mathrm{B}+\beta^{+}+\mathrm{X}\)
Then the unknown particle \(X\) is:
1. neutron 
2. antineutrino
3. proton 
4. neutrino

The minimum wavelength of X-rays produced by electrons accelerated by a potential difference of V volt is equal to 

1. $\frac{eV}{hc}$ 

2. $\frac{eh}{cV}$ 

3. $\frac{hc}{eV}$ 

4. $\frac{cV}{eh}$

The energy released by the fission of one  uranium atom is 200 MeV. The number of fission per second required to produce 3.2 W of power is (Take, 1 eV = 1.6$\times$${10}^{-19} J$) 

1. ${10}^7$ 

2. ${10}^{10}$ 

3. ${10}^{15}$

4. ${10}^{11}$

The binding energy of deuteron is 2.2 MeV and that of ${}_2{}^{4}He$ is 28 MeV. If two deuterons are fused to form one ${}_2{}^{4}He$, then the energy released is 

1. 25.8 MeV

2. 23.6 MeV

3. 19.2 MeV

4. 30.2 MeV

Half-life of a radioactive substance is 12.5 h and its mass is 256 g. After what time, the amount of remaining substance is 1 g? 

1. 75 h

2. 100 h 

3. 125 h

4. 150 h

The nucleus ${}_6{}^{12}C$ absorbs an energetic neutron and emits a beta particle $\left({\beta }^{-}\right)$. The resulting nucleus is 

1. ${}_7{}^{14}C$

2. ${}_7{}^{13}N$ 

3. ${}_5{}^{13}B$ 

4. ${}_6{}^{13}C$

If in a nuclear fusion  process, the masses of the fusion nuclei be $m_1 and m_2$ and the mass of the resultant nucleus be $m_3$, then 

1. $m_3=m_1+m_2$

2. $m_3=\left|m_1-m_2\right|$

3. $m_3<\left(m_1+m_2\right)$ 

4. $m_3>\left(m_1+m_2\right)$

If $N_0$ is the original mass of the substance of half life period $T_{1/2}$= 5 years, then the amount of substance left after 15 years is

1. $N_0$/8 

2. $N_0$/16

3. $N_0$/2

4. $N_0$/4