What % of benzol peryoxide should be used for treating acne n scars and should it be used in cream or in lotion base for oily skin?

Varies: Different people can tolerate different strengths of benzoyl peroxide on their skin. Some people are allergic and cannot tolerate it at all. Most people can tolerate 2.5% to 3%. However, higher strengths up to 10% are more effective, especially on the back. Consult a dermatologist who will work with you to devise a safe and effective regimen personalized for your skin.