Explanation:

What is most probable speed?

Most probable speed is the speed at which the maximum number of molecules in a gas have that speed. It is denoted by Vmp.

What is the formula for most probable speed?

Vmp = √(2kT/m)

where k is the Boltzmann constant, T is the temperature, and m is the mass of a molecule.

Given:

Mass of H2 gas, m = 8g

Most probable speed of H2 gas, Vmp = 200m/s

What is the kinetic energy of a gas?

Kinetic energy of a gas is the energy a gas possesses due to the motion of its molecules.

Kinetic energy (KE) = 1/2mv^2

where m is the mass of a molecule and v is its velocity.

What is the average kinetic energy of a gas?

Average kinetic energy of a gas is the average of the kinetic energies of all the molecules in the gas.

Average kinetic energy (KEavg) = (3/2)kT

where k is the Boltzmann constant and T is the temperature.

What is the formula to find the mass of a molecule?

Mass of a molecule (m) = mass of gas / Avogadro's number

where Avogadro's number = 6.022 x 10^23

Calculations:

Mass of H2 gas, m = 8g

Avogadro's number = 6.022 x 10^23

Mass of a molecule (m) = 8g / 6.022 x 10^23 = 1.332 x 10^-22 kg

Most probable speed of H2 gas, Vmp = 200m/s

Using the formula Vmp = √(2kT/m), we can find T.

T = mVmp^2 / (2k) = 1.332 x 10^-22 x (200)^2 / (2 x 1.38 x 10^-23) = 4.8 x 10^2 K

Now, using the formula KEavg = (3/2)kT, we can find the average kinetic energy.

KEavg = (3/2) x 1.38 x 10^-23 x 4.8 x 10^2 = 1.2 x 10^-20 J

Therefore, the average kinetic energy of H2 gas is 1.2 x 10^-20 J.

Answer:

The correct option is (c) 120 J.