Answer:
The importance of international bureau of weights and measures are;
1. to bring unification of measurement system.
2. to establish and preserve fundamental international prototypes.
3. to verify national standards, etc.
It is called absorption spectrum because a gas of hydrogen will make a line spectrum and if viewed for another angle it would be between a continuum light and a emission line spectrum
Burning of gases is one the example of chemical change
It is basically shielding a magnetic field. This can be done with rubber or any other material that is thick. Normally small magnets already block the shield.
