Nuclear fission is the phenomenon of splitting of a heavy nucleus into two or more lighter nuclei. Nuclear fussion is the phenomenon of fusing two or more lighter nuclei to form a single heavy nucleus. In both these processes, a certain mass \(\left( \Delta m \right) \) disappears, which appears in the form of nuclear energy, \(E=\left( \Delta m \right) { c }^{ 2 }.\) The release of energy is so sudden that it cannot be controlled. This causes havoc. Nuclear fission is the basis of an atom bomb and nuclear fusion is the basis of a nydrogen bomb. A powerful device, called Nuclear Reactor has been developed, where in nuclear energy produced is utilised for constructive purposes.
Read the above passage and answer the following questions:
(i) How much energy is released in the fission of one nucleus of \({ U }^{ 235 }\) and in how much time?
(ii) Give an estimate of devastation potential of an atomic explosion.
(iii) Should we ban nuclear research in this field? Give your views briefly.

Natural radioactivity is a spontaneous and self disruptive activity exhibited by a number of heavy elements in nature. Thus a heavy element disintegrates by itself without being forced by any external agent to do so.
According to radioactive decay law, the number of atoms disintegrated per second (i.e., rate of disintegration of radioactive atoms) at any instant is directly proportional to the number of radioactive atoms actually present in the sample at that instant, i.e., \(-\frac { dN }{ dt } \propto N \ or \ R=-\frac { dN }{ dt } =\lambda N,\) where is \(\lambda \) decay constant.
Read the above passage and answer the following questions :
(i) The count rate from a radioactive sample containing \({ 10 }^{ 16 }\)  atoms is \(4\times { 10 }^{ 16 }\)  per second. What is the value of decay constant?
(ii) Name the three types of radiactive radiations. Which one of them is most penetrating?
(iii) What does radioactive decay law imply in day to day life?

According to Bohr's theory of hydrogen atom, total energy of electron in a stationary orbit is \(E=-\frac { 13.6 }{ { n }^{ 2 } } eV,\) where n is the number of orbit. Clearly, total energy of electron in a stationary orbit is negative, which means the electron is bound to the nucleus and is not free to leave it. An n increases, value of negative energy decreases, i.e., energy is progressively larger in the outer orbits.
Read the above passage and answer the following questions :
(i) What is total energy of electron in ground state of hydrogen atom? What does it imply?
(ii) Energy required to remove an electron is smaller when atoms is in any one excited state. Comment.
(iii) How is this concept translated in day to day life?

Ajeet's younger brother was just seeing class 12th books. He wondered to know the structure of atoms and arrangement of electrons and protons in them. As he was a class 6th student, he did not understand the whole concept of atomic structure. Ajeet helped him to understand the structure of atoms.
Read the above passage and answer the following questions:
(i) What are the values shown by Ajeet?
(ii) On which metal Rutherford performed \(\alpha \) - particles scattering experiment?
(iii) How Rutherford concluded that at the centre of atom there is massive nucleus which contains positive charge?

On the basis of Bohr's theory of H-atom, total energy of electron in a stationary orbit is given by the relation
Where, n is the number of orbits. It is clear that total energy of electron in a stationary orbit is negative which implies that electron is bound to the nucleus and is not free to leave it. The value of negative energy decreases as n increases.
Read the above p[assagr and answer the following questions:
(i) What is the total energy of electron in ground state of hydrogen atom? What does it indicate?
(ii) Why does energy required to remove an electron is smaller when atom is in any one excited state?