mP and mn are masses of proton and neutron respectively. An element of mass m has Z protons and N neutrons, then
1. m>Zmp+Nmn
2. m=Zmp+Nmn
3. m<Zmp+Nmn
4. m may be greater than, less than or equal to Zmp+Nmn, depending on the nature of the element.
The nuclei C136 and N147 can be described as [1990]
1. isotones
2. isobars
3. isotopes of carbon
4. isotopes of nitrogen
The radioactivity of a sample is A1 at a time t1 and A2 at time t2. If the mean life of the specimen is T, the number of atoms that have disintegrated in the time interval of t2-t1 is:
1. A1-A2
2. A1-A2T
3. (A1-A2)T
4. A1t1-A2t2
What is the radius of iodine atom? (atomic no. 53, mass no. 126) [1988]
1. 2.5×10-11 m
2. 2.5×10-9 m
3. 7×10-9 m
4. 7×10-6 m
Which of the following statements is true for nuclear forces? [1990]
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 relationship between disintegration constant [λ] and half-life [T] will be:
1. λ=log10 2T
2. λ=loge 2T
3. λ=Tloge 2
4. λ=log2 eT
Alpha particles are
1. 2 free protons
2. helium atoms
3. singly ionized helium atoms
4. doubly ionised helium atoms
A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier?
1. 1.0 microcurie
2. 0.5 microcurie
3. 4 microcurie
4. 8 microcurie
A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain?
1. 12
2. 116
3. 18
4.1256