State whether the given collection is a set or not?

Rich people living in Delhi.

State whether the given collection is a set or not?

Ten countries of Europe.

State whether the given collection is a set or not?

States of India whose names start with letter $M$.

State whether the given collection is a set or not?

All intelligent students of your school.

State whether the given collection is a set or not?

All the I.C.S.E. Schools in India.

Write the set in roster form.

$A=\{x\mid x$ is a letter of the word $\text{'}\mathrm{number}\text{'}$$\}$

Write the set in roster form.

$B=\{x\mid x$ is a positive perfect cube number less than $30\}$

Write the set in roster form.

$\{$Prime factors of $24\}$

Write the set in roster form.

$\mathrm{D}=\{x\mid x$ is a colour of the rainbow$\}$