Question

sometime the rail track become curve explain why this happen how can the situation be avoided

Answer 1

its just bcoz of the high temperature and we all know that tracks are made up of iron so due to the high temperature iron used to spread so thats the main reason behind that why the rail track become curve
yes the situation can be avoided by using giving them bit more space between them
or by using heat convecters or by making the track of any other material like steel
hope will help :)