Question

Chemical laws obeyed by all gases are:
(A) Avogadro’s Law
(B) Graham’s Law
(C) Dulong and Petit’s Law
(D) Boyle’s Law

Answer 1

Dulong and Petit’s Law states that the product of atomic mass and specific heat of a solid element is approximately equal to $6\cdot 4$ cal/mol. This law is valid for solid elements so the gases do not obey this law. All the other three laws are applicable to gases.

Complete Step By Step Solution
Boyle’s Law describes the inverse proportional relationship between pressure and volume at a constant temperature and a fixed amount of gas. This law came from a manipulation of the Ideal Gas Law. Boyle’s Law was given by Robert Boyle in 1662. According to Boyle’s Law- ${{P}_{1}}{{V}_{1}}={{P}_{2}}{{V}_{2}}$ Where the index 1 is for first gas and index two is for second gas at constant temperature.
According to Avogadro’s Law under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules. This law gives- $\dfrac{{{V}_{1}}}{{{n}_{1}}}=\dfrac{{{V}_{2}}}{{{n}_{2}}}$ at same temperature and pressure conditions. Here, ${{n}_{1}}$ and ${{n}_{2}}$ are the no. of moles for gas 1 and gas 2 respectively.
Graham’s Law of Diffusion states that the rate at which gases diffuse is inversely proportional to the square root of their densities. This is given by- $\dfrac{{{r}_{1}}}{{{r}_{2}}}=\sqrt{\dfrac{{{\rho }_{2}}}{{{\rho }_{1}}}}$
For effusion, the rate of effusion of gases is inversely proportional to the square root of their molar masses. This is given by- $\dfrac{{{r}_{1}}}{{{r}_{2}}}=\sqrt{\dfrac{{{M}_{2}}}{{{M}_{1}}}}$
Dulong–Petit law states that the gram-atomic heat capacity of an element is constant i.e. it is the same for all solid elements, about six calories per gram atom. This law is not applicable for gases.
So, all the three laws except Dulong’s-Petit’s law are obeyed by the gases.
Therefore, the correct choices are (A), (B) and (D).

Additional Information
Boyle’s Law has many real life applications. It is quite useful for Scuba Divers. As they dive deeper, the pressure on their body increases and the volume in their lungs decreases. As they ascend out of the depths of the ocean, they slowly release air from their lungs, which is compressed due to the pressure. It has an application in the filling of bike tyres and many more such real life applications.

Note
An ideal gas law is formed by combining Boyle’s law, Avogadro law and Charles’s law. It is given by $PV=nRT$ . An ideal gas is a hypothetical gas in which intermolecular forces do not exist to complicate the simple Ideal Gas Law. The term $\dfrac{PV}{nRT}$ is called the compression factor and it is a measure of the ideality of the gas. An ideal gas will always equal 1 when plugged into this equation. The greater it deviates from the number 1, the more it will behave like a real gas rather than an ideal.