The length of each rail is 10m. The linear expansion of steel is  0.000012/0C and the range of variation of temperature at the given place is  150C. So the gap to be provided between the rail is

change in length due to variation in temperature is Δl=lαΔt here l is initial length=10m;α is coefficient of linear expansion=12×10−6/C  0 Δt is change in temperature=150C Δl=10×12×10−6×15 Δl=180×10−5=18×10−4 Δl=0.0018m=gap between 2 rails to be maintained