(i) Ron sells 5 pens for $4, which means the selling price of each pen is $4/5 = $0.8.
(ii) Ron bought each pen for $1 and is selling each pen for $0.8, so he is suffering a loss of $1 - $0.8 = $0.2 on each pen.
(iii) Ron bought 250 pens at $1 each, so his total cost was 250 x $1 = $250. He is selling each pen for $0.8, so his total revenue from selling all the pens is 250 x $0.8 = $200.
Therefore, Ron's total loss is his total cost minus his total revenue, which is $250 - $200 = $50. So Ron suffered a loss of $50 by selling all the pens.