Hi, of you're giving kvpy in 11th that means you'll be giving kvpy for the first time, i.e. the first stage so you'll have to answer all PCMB questions, that being said even if you do not answer even one biology question in it and prepare really well for PCM part you can easily get selected for the next round. And then when you give kvpy in 12th that is second year you can choose from PCM or PCB. But biology is pretty high scoring, you can easily get those 20-25 marks with just going through the subject once and it'll get you a good rank too. The rest is up to you if you don't want to give biology then make sure your PCM is really strong. Thank you and all the best.