Hello Student

For appearing one subject of mathematics in 12 science as combination candidates can appear in one subject examination in in CBSE improvement examination. The other hand here the candidate or student can appear in in NIOS system of education that is National Institute of Open schooling of one subject or more. In this system of education candidates when  feel that he or she is ready to appear for examination he will walk in for Examination to the nearest  centre and express his or her feelings and the authority will take his or her examination of one or more subjects as he or she likes. On the other hand IGNOU Indira Gandhi National Open University  has the system of appearing one subject of 12 science like mathematics or any other subjects for single paper choice.

Hope this will help.

Hello Student

This is possible  in case of improvement exam of CBSE for appearing one subject like mathematics. Aadhar and you can do it it from IGNOU and new National Institute of Open schooling system. Hindi news candidate can choice his attempt and schedule of appearing in the examination when he or she will be feeling that she or she is prepared for appearing examination.