1)Pitch is measure of the of sound. (a) amplitude (b) wavelength (c) time period (d) frequency

2)A book placed on a shelf can be seen from any part of that room due to .

(a) regular reflection

(b) clear reflection

(c) diffused reflection

(d) parallel reflection

3)Two mirrors A and B are placed at right angles to each other. A ray of light incident

on mirror A at an angle of 25° falls on mirror B after reflection. The angle of reflection

for the ray reflected from mirror B would be

1) wave length

2) parallel reflection

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.