Statements:

Only wires are switches.

No wire is a board.

Only nuts are boards.

Conclusions:

I. All switches are wires.

II. All boards are nuts.

III. All nuts are boards.

IV. No switch is a board.

Solution

Only wires are switches can be written in two ways = Some wires are switches (I) and All switches are wires (A). Hence, conclusion I will follows. Only nuts are boards ⇒ All boards are nuts. Hence, conclusion II will follows. Only nuts are boards = Some nuts are boards (I) and All boards are nuts (A). Hence, conclusion II will follow but conclusion III will not follow. Only wires are switches⇒ All switches are wires & no wire is a board. Hence, conclusion IV will follows. Aletrnate Method: Only wires are switches ⇒ All switches are wires (A). Hence, conclusion I will follows. Only nuts are boards ⇒ All boards are nuts. Hence, conclusion II will follows. All boards are nuts (A) ⇒  Hence, conclusion II will follow but conclusion III will not follow. Only wires are switches⇒ All switches are wires & no wire is a board. Hence, conclusion IV will follows.