is droppining one year for preparation after 12th for engineering is ok ya not?

It's only OK if you really spend that year preparing.

Most people find it easier to prepare by going straight to school. And remember, the first year of any engineering curriculum is going to be spend in background and preparation...math, physics, chemistry, even composition so that one can learn to express oneself adequately. The real engineering usually doesn't start until the second year, and even that is pretty basic stuff (Elementary circuits for electrical engineers, principles of statics and dynamics for mechanical engineers, etc.)

the first answer is right on the money here,

There is nothing that says you can't go back to school later, I just graduated in 06 with an engineering degree and about half of my classmates had taken at least a year or two off from school.

However, you don't need to spend a year studying, college will pick up right where high school left off, taking a year off makes it harder to remember what you learned.

If you aren't sure that engineering is for you, or you just want to take it slow to start with, go to a community college first, get into the math, physics and engineering courses and have a plan for which university you want to transfer to, this way if you decide to give up on engineering you will have saved lots of tuition verses going to a big university.

Good Luck.