Opening a trading account requires you to go through a process called Know Your Client or KYC, which includes submission of key documents to the broker along with the account opening form.
There can be various reasons for trading account closing. Normal, trading account closing is done when you don’t want to operate in stock markets any longer or don’t want to trade through that broker any longer.
A demat account is necessary to hold your financial securities today. This account not only lets you hold your securities, but also lets you transact, i.e. buy or sell, these securities.