7 moles of a tetra-atomic non-linear gas 'A' at 10 atm and T K are mixed with 6 moles of another gas B at `(T)/(3)K` and 5 atm in a closed, rigid vessel without energy transfer with surroundings. If final temperature of mixture was `(5T)/(6) K,` then gas B is ? (Assuming all modes of energy are active)