The correct options are
A Raju sells a chocolate worth ₹8 for ₹10.
B Harshit buys a ₹20 worth pen for a discounted rate of ₹15
C Raju got an extra ₹1 by selling a ₹8 chocolate for ₹9.
Economics is a subject that studies the cost of manufacturing, buying and selling things. If you are trying to understand the impact of money in any situation, you are dealing with economics.