I'm newbie and want to learn more from this forum.I want to know that How many topic I should post per day for getting ?which is the best topic for getting more merit ?
If you want to learn then read (lurk) for as much time as necessary. You ought to post when you can answer a question or when you have a question.
The number of posts you have will be a reflection of the above and you'll get merit when you write good posts.
This forum has become inundated with spammers and people writing silly, irrelevant posts that don't add to the site simply to up their reputation. The moderators are thankfully trying to limit this.