Answer:
the energy of the third excited rotational state 
Explanation:
Given that :
hydrogen chloride (HCl) molecule has an intermolecular separation of 127 pm
Assume the atomic isotopes that make up the molecule are hydrogen-1 (protium) and chlorine-35.
Thus; the reduced mass μ = 
μ = 
μ = 
∵ 1 μ = 1.66 × 10⁻²⁷ kg
μ = 
μ = 1.6139 × 10⁻²⁷ kg

The rotational level Energy can be expressed by the equation:

where ;
J = 3 ( i.e third excited state) &




We know that :
1 J = 



I think it is the gas and the heat in it
The SI unit for amount<span> of </span>substance<span> is the </span>mole<span>. It has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant. The </span>mole<span> is defined as the </span>amount<span> of </span>substance that contains<span> an equal </span>number<span> of elementary entities as there are </span>atoms in 12g<span> of the </span>isotope<span> carbon-</span>12<span>.
Hope This Helped! :3</span>
Protons = 20
Electron = 20
Neutrons = 20
Hope this Helps :)