पारंपरिक रूप से नैदानिक (क्लिनिकल) और प्रयोगशाला थर्मामीटरों में किस तरल धातु का उपयोग किया जाता है?

Small gaps are deliberately left between consecutive steel rails on a railway track to:

Given below are two statements, one labeled as Assertion (A) and the other as Reason (R). Select the correct answer from the options below. Assertion (A): A very hot glass cracks when cold water is poured onto it. Reason (R): Glass expands when heated and contracts when cooled.