Hello student!!
Yes you can apply for DRDO if you have PCM group but you need to complete graduation before applying for DRDO admission.
To take admissions in DRDO you should

• After 12th from PCM subjects Candidates should have passed a Bachelor's Degree in Science/ 3-years Diploma in Engineering/Technology/Computer Science/allied subjects in required discipline from a recognized Institute. Candidates who are pursuing their final year degree in any stream are also eligible to apply for DRDO .
• For the SET exam, you can to apply online through the official website of DRDO.
• Fill the DRDO online application form and apply for exam.

Hey !
Folloeing is the eligibility criteria for DRDO , Candidates should have a Bachelor's degree in Science or a 3-years Diploma in Engineering/Technology/Computer Science/allied subjects in the required discipline from a recognized institute. Candidates who are pursuing their final year degree in any stream are also eligible to apply forDRDO . So if you are talking about PCB in class 12 , sothat doesn't bother here if you satisfy the above mebtioned criteria