I am designing database for accounts managment system for toys shop which
Purchases Items from supplier and sell to customers on credit or cash.
After specified time toy shop recieve payment from customers and pay dues to its supplier (in case of credit)
Deposit & Withdraw cash from bank
Expenses

In ERD diagram there are two option for Sale & Purchase
Option 1
Sale
SaleLine
Purchase
PurchaseLine
Option2
Order (Include attribute OrderType=Purchase/Sale)
OrderLine

Which Option is correct ??

which option meets your business requirement?
think the process through
imagine . try to understand what is required
develop your model so it meets that requirement.

ultimately, providing you can explain the reasons for your choices in your assignment then it doesn't matter. its about you demonstrating that you understand the process, not about you presenting a finished model with no understanding of how the finished model was designed