Questions

The Doppler effect or Doppler shift is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. 

The United Nations Public Service Day is observed every year on June 23 to recognize the work of public servants and to encourage young people to pursue careers in the public sector. The day is also observed to celebrate value and virtue of public service to the community and to raise awareness regarding the contribution of public service in the development of society and honouring the work of public servants.

Ideal Gas Law ::

The Combined gas law or General Gas Equation is obtained by combining Boyle's Law, Charles' Law, and Gay-Lussac's Law. It shows the relationship between the pressure, volume, and temperature for a fixed mass (quantity) of gas:

P1V1T1 = P2V2T2

Hence, the Boyle's law P1V1 = P2T2, relates to ideal gas equation.

Hydrogen is the common element to all Acids. But every element which contains Hydrogen is not an Acid. Most of the acids also contain Oxygen.

Here in the given options, The girl, whom you have met yesterday is my sister is the sentence which has relative pronoun.

The pronoun which is used to connect a clause or phrase to a noun or pronoun is called as relative pronoun.

The most common relative pronouns are who, whom, whose, which, and that. Sometimes when and where can also be used as relative pronouns.