Questions

Harappa was the earliest city discovered in India.

It is Blackboard or Chalkboard which is Black when clean, and as you write on it with white chalk it becomes dirty in White color.

Here the most stable carbocation is the option (2).

Carbocations are always hungry for electrons. The stability of carbocations increases from primary to secondary to tertiary. Here, option (c) shows the most stable carbocation because it can easily withdraw electrons from two other carbon atoms and the more electronegative oxygen atom.

Carbocation stability depends on hyperconjugation. The tertiary carbocation is stabilized by electron releasing inductive effect.