Having "Kumar" in your Aadhar card and not in your 10th & 12th certificates might cause minor inconveniences while applying for government jobs, but it shouldn't be a major hurdle.

This is considered a minor mismatch as "Kumar" is a common middle name and doesn't significantly alter your identity.

You can get your Aadhaar card updated to reflect the same name as your certificates. This process is relatively simple and can be done online or by visiting an Aadhaar Seva Kendra. You need documents like your PAN card, Voter ID, or passport as proof of your identity.

If updating your Aadhaar card seems time-consuming, you can prepare an affidavit from a notary public. This affidavit should declare that "Kumar" in your Aadhaar card is the same person mentioned by name and surname in your certificates. You might need this affidavit along with your certificates while applying for government jobs.

Having "Kumar" in your Aadhaar card can be rectified. Updating your Aadhaar card is the ideal solution, but an affidavit can serve as a temporary measure while you get your Aadhaar card updated. It's best to address this mismatch before applying for government jobs to avoid any delays or complications.

I hope it helps!