and are masses of proton and neutron respectively. An element of mass m has Z protons and N neutrons, then
(4) m may be greater than, less than or equal to , depending on the nature of the element.
The nuclei can be described as 
(1) isotones (2) isobars (3) isotopes of carbon (4) isotopes of nitrogen
The radioactivity of a sample is at a time and at time . If the mean life of the specimen is T, the number of atoms that have disintegrated in the time interval of is:
(1) (2) (3) (4)
Three fourth of the active nuclei decay in a radioactive sample in 3/4 s. The half-life of the sample is
(1) (2) 1 s (3) (4)
Which of the following statements is true for nuclear forces? 
(1) They obey the inverse square law of distance.
(2) They obey the inverse third power law of distance.
(3) They are short range forces.
(4) They are equal in strength to electromagnetic forces.
The ratio of the radii of the nuclei and is approximately 
(1) 6 : 10 (2) 13 : 52 (3) 40 : 177 (4) 14 : 73
Bragg's law for X-rays is
(1) d sin = 2 n (2) 2d sin = n
(3) n sin = 2 d (4) None of these
Alpha particles are
(1) 2 free protons
(2) helium atoms
(3) singly ionized helium atoms
(4) doubly ionised helium atoms