When a radioactive substance emits an $\mathrm{\alpha }$-particle, its position in the periodic table is lowered by

(1) One place             

(2) Two places

(3) Three places           

(4) Four places

If a radioactive substance reduces to $\frac{1}{16}$ of its original mass in 40 days, what is its half-life 

(1) 10 days           

(2) 20 days

(3) 40 days           

(4) None of these

The electron emitted in beta radiation originates from

(1) Inner orbits of atoms

(2) Free electrons existing in nuclei

(3) Decay of a neutron in a nucleus

(4) Photon escaping from the nucleus

A radioactive nucleus with Z protons and N neutrons emits an $\mathrm{\alpha }$-particle, 2$\mathrm{\beta }$-particles and 2 gamma rays. The number of protons and neutrons in the nucleus left after the decay respectively, are 

(1) Z – 3, N – 1                 

(2) Z – 2, N – 2

(3) Z – 1, N – 3                 

(4) Z, N – 4

A radioactive nucleus emits a beta particle. The parent and daughter nuclei are 

(1) Isotopes             

(2) Isotones

(3) Isomers               

(4) Isobars

The S.I. unit of radioactivity is 

(1) Roentgen         

(2) Rutherford

(3) Curie               

(4) Becqueral

The half-life of a radioactive substance against $\mathrm{\alpha }$-decay is $1.2\times {10}^7$ s. What is the decay rate for $4\times {10}^{15}$ atoms of the substance

(1) $4.6\times {10}^{12}<mspace\; width="1em"></mspace>\mathrm{atoms}/\mathrm{s}$         

(2) $2.3\times {10}^{11}<mspace\; width="1em"></mspace>\mathrm{atoms}/\mathrm{s}$

(3) $4.6\times {10}^{10}<mspace\; width="1em"></mspace>\mathrm{atoms}/\mathrm{s}$          

(4) $2.3\times {10}^8<mspace\; width="1em"></mspace>\mathrm{atoms}/\mathrm{s}$

In a sample of radioactive material, what percentage of the initial number of active nuclei will decay during one mean life 

(1) 69.3%           

(2) 63%

(3) 50%               

(4) 37%

99% of a radioactive element will decay between

(1) 6 and 7 half lives             

(2) 7 and 8 half lives

(3) 8 and 9 half lives             

(4) 9 half lives