The variation of the decay rate of two radioactive samples A and B with time is shown in the figure.

Which of the following statements are true?

(a) Decay constant of A is greater than that of B, hence A always decays faster than B
(b) Decay constant of B is greater than that of A but its decay rate is always smaller than that of A
(c) Decay constant of A is greater than that of B but it does not always decay faster than B
(d) Decay constant of B is smaller than that of A but still its decay rate becomes equal to that of A at a later instant

1. (a, b)

2. (a, c)

3. (b, d)

4. (c, d)

Graph given below shows the variation of binding energy per nucleon, E_bn as a function of mass number. For nuclei with mass number A such that, 30 < A < 170, E_bn is almost constant because nuclear forces are:

1. Short-ranged 

2. Medium-ranged

3. Long-ranged

4. None of the above

Graph gives the variation of potential energy of a pair of nucleons as a function of their separation, r. From the graph it can be concluded that the force between nucleons is attractive for distances:

1. Less than r_o

2. Greater than r_o

3. Less than $\frac{r_o}{2}$

4. Less than $\frac{r_o}{4}$

The graph shows the exponential decay of a radioactive specie. The number of nuclei decayed after time t is:

$$\begin{gathered} 1. N_o{e}^{-\lambda t} \\ 2. 2N_o{e}^{-\lambda t} \\ 3. N_o-N_o{e}^{-\lambda t} \\ 4. 2N_o-N_o{e}^{-\lambda t} \end{gathered}$$