All fires require oxygen () There is no oxygen in that room (T) .
Therefore, there is no fire in that room.
A. valid, and Sound.
B. valid, and Unsound.
C. invalid and Sound
D. invalid , and Unsound

The sentences are invalid and unsound.

The fire is defined as the vigorous oxidation of a substance. Now oxidation can occur in presence of any oxidising agent. Like magnesium in presence of nitrogen in high temperature with a dazzling brownish flame to produce magnesium nitride. So fire can be produced in absence of oxygen.

Oxygen is present everywhere in world. So production of a whole room without oxygen is very tough to produce and costly process. So its very unsound.