My brother failed in class 12 pcm so for him diploma in mechanical eng will be right or not.

Hello Akshat. Well it all depends upon the interest of your brother. Diploma course will give you hands-on practical experience, when you complete the course. After diploma, if your brother enrolls for engineering as lateral entry, he will be benefitted will diploma.

Both mechanical and computer science are equally good and have great scope. So it boils down to your brother's interest.

All the best.