I want to write off cash what entries should I pass in journal or what is contra account for cash write off?

Write-off cash? This does not make sense. You can write off cash due to you in the form of a receivable. But to write off cash (i.e. to say it was lost or stolen), would have to hit either a gain/loss account if the write-off affects the current period or retained earnings if it relates to a prior period adjustment.