1. If a radioactive material decays with a half-life of one year, what's the fraction of the material that will remain after five years?

1/5

1/10

1/16

1/32

1/50
Ans:(1/2)*(1/2)*(1/2)*(1/2)*(1/2)=1/32.

2. i) Which of the forces is the strongest between two protons separated by 10*E-15 m? a) Strong, b) electromagnetic, c) gravitational ?

ii) i) Which of the forces is the strongest between two protons separated by 10*E-10 m? a) Strong, b) electromagnetic, c) gravitational ?

Explain your reason/s.
Ans:i)Strong force, ii) electromagnetic force; because of strong force is short ranged and beyond the nuclear size, it is not active, only electromagnetic force is primary.

3. A certain fissionable material X undergoes nuclear fission when hit with a slow neutron. The fission products are  ₃₇Rb⁹³  +  ₅₅Cs¹⁴¹ + 2n , what is X ?
Ans:X is ₉₂U²³⁵