Dear Ritu,
Please note that Bonus is nothing but in the first instance a profit sharing by the employer for the effort of the employees. as far as the law is concerned all the organization who have completed 5th year of its inception must irrespective of its profit/Loss must give bonus (Min-8.33%,Max-20%) this will be done through a concept of Set-on and Set-off.
Every worker must be compulsorily give bonus but when it goes to staff especially high paid staff ,they are paid as ex Gratia which the organization gives as profit sharing or whatever concept it may have.
In some case as you have said they are shown in CTC which in case their is any higher benefit shall be paid upon to employees as to motivate them. Basically we have to look into the policy and compensation structure when we do this kind of payment for the high paid employees of the organization.
Hope its clear further clarification can post your queries. | 
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