Purchase of cartridge is expense or fixed asset

Printing & stationery expense.

anything whose useful life is less than 12 months is regarded as an expense. and whose life exceeds 12 months is regarded as a fixed asset. hence, the cartridge's useful life is less than 12 months that's why it is a revenue expenditure.

Day to day operating expenses are expensed as well and not capitalised.

its consumable so should be book under Printing & Stationery head not in FA