Questions

The demand curve facing a perfectly competitive firm is a horizontal straight line equal to the equilibrium price of the entire market because a perfectly competitive firm can sell all units brought to market at the same price.

The error is in third part. By using ‘not’ after ‘unless’, both the negatives cancel each other. So, the correct usage will be ‘unless he reports for duty immediately’. Since “unless” is negative it should be
followed by affirmation, like “unless he reports for duty”. Incase “unless” was absent, we could have written “if he does not report” and expressed the same meaning.