Question

give reasons for gaps left in railway tracks

Answer 1

When railway tracks are laid the engineers leave a small gap between two rails. All metals expand when heated. If two railway tracks are laid together without any gap between them they will push against each other when they expand in the day time because of the heat of the sun, and when they cool down in the night they will contract and return to their original state pulling against each  other.  
I hope it helps you
please mark me as brain list answer please please please please please

Answer 2

It is done to prevent accidents. During day time metals expands and at night it comes to its original shape. If not done so it may bend on heating and can cause accidents.

Hope it helps!!!