Solution:Case (a): X is an. unpaid seller because the full price has not been .paid.Case (b): X is an unpaid seller because the cheque received as conditional payment has been dishonoured.Case (c): X is not an unpaid seller because the credit period has not yet expired and the buyer has not yet become insolvent.Case (d): X is an unpaid seller because the price remains unpaid even after the expiry of credit period.Case (e): X is an unpaid seller because the buyer has become insolvent