We treat closing stock as an asset, and recognise it in the balance sheet and show it in the credit side of Trading account as goods unsold at the end of the year. But as we know last year's closing stock is the opening stock for the current year,

Then why we treat opening stock as an expense (debit side of trading account) in current year's trading account and closing stock as an asset?

Can you please define what you mean by "stock." It certainly doesn't sound like you're talking about stock the equity account. Also, what are you calling a "trading account." What kind of account is that?

This may be some subject that I am unfamiliar with and maybe someone else can help you better. But also different books, companies, etc. can use different names for things, very common things and I just don't recognize their name. So perhaps if you can tell me what they are, this might make sense to me.