Question

when silk is burnt ,it smells like burning hair however, when cotton is burnt, it smells like burning paper why

Answer 1

this is because of the difference in material of these 2 cloth. The components are different and thus they release different smells on burning

Answer 2

Paper is made out of plants.Cotton is also made out of plants.So they both give the similar fumes while burning as their origin comes from plants
silk is made out of silkworms.They create hair like fibers which are woven to form silk fabric.That's why it gives hair burning smell.