I am not good in using blender so i wanted to ask if it is possible to make an object with just one triangle and how would it look like, will the no of triangle increase if you scale it up.
A mesh with just a single triangle is perfectly possible.
It would look like a triangle. Nothing particularly surprising.
Scaling it up won't automatically add more triangles, unless you use something like a tessellation shader to dynamically subdivide it.
It sounds like you might be trying to do something more involved though — if you edit your question to describe the problem you're trying to solve or the ultimate effect you want to use this to achieve, we might be able to give you a more constructive answer.