MCB

 MCB stands for 

a) miniature circuit board 

b) miniature circuit band

c) miniature circuit breaker

d) miniature circuit blocker

Ans: c

RADIOACTIVITY

Q1: What is radioactivity?

A:  The  phenomenon of spontaneous emission of alpha particle or beta particle and gamma rays  from an unstable nucleus is called radioactivity. 

 Q2: When does a nucleus  become unstable ?

A: When the number of neutrons become much more than that of protons.

Q3: Which part of the atom takes part in radioactivity ?

A: Nucleus

Q4: What happens to the radioactive behaviour of a radioactive sample if it is chemically oxidized ?

A: The radioactive behaviour does not change. As oxidation is the chemical change, it does not affect the nuclear activity.

Q5: How does the atomic number and mass number change if a radioactive nucleus releases one alpha particle ?

A: Atomic number decreases by 2 and mass number decreases by 4

Q6: How does the atomic number and mass number change if a radioactive nucleus releases one beta particle?

A: Atomic number increases by 1 and mass number does not change.