Questions

Diamond is the hardest substance available on Earth.

Diamond is the hardest substance available on Earth due to the giant molecular structure of diamond in which each carbon atom is covalently bonded to four other carbon atoms. A covalent bond is very strong and requires a large amount of energy to break itself, and diamond has many covalent bonds.

It belongs to the field of Fashion Designing

Yeast used in making bread is a Fungus.

We know that, in computers transformation of input into output is performed by the ALU unit i.e, the Arithematic and Logical unit that performs all the logical and arithmatical operations in the CPU - Central Processing Unit.

Relegate means Assigning an inferior rank or position to. That means, downgrading or pulling down, lower a person.

All other options have words with opposite in meaning.

Hence, Relegate is an English word which is similar in meaning to Downgrade.