The rate of disintegration of a fixed quantity of a radioactive substance can be increased by:

1. increasing the temperature.

2. increasing the pressure.

3. chemical reaction.

4. it is not possible.

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$) [WB JEE 2010]

1. ${10}^7$ 

2. ${10}^{10}$ 

3. ${10}^{15}$

4. ${10}^{11}$

The power obtained in a reactor using $U^{235}$ disintegration is 1000 kW. The mass decay of \(U^{235}\) per hour is:

1. 1 microgram           

2. 10 microgram       

3. 20 microgram     

4. 40 microgram

Light energy emitted by stars is due to

1. Breaking of nuclei 

2.Joining of nuclei       

3. Burning of nuclei

4. Reflection of solar light

The constituents of atomic nuclei are believed to be [1991]

1. neutrons and protons

2. protons only

3. electrons and protons

4. electrons, protons and neutrons

The half-life of radium is about 1600 yr. Of 100 g of radium existing now, 25 g will remain unchanged after [2004]

1. 4800 yr

2. 6400 yr 

3. 2400 yr

4. 3200 yr

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? [2001]

1. 75 h

2. 100 h 

3. 125 h

4. 150 h

A radioactive substance disintegrates 1/64 of initial value in 60 s. The half-life of this substance is

1. 5 s 

2. 10 s

3. 30 s 

4. 20 s

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 [2004]

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. $m_3>\left(m_1+m_2\right)$