If X={a,e,I,o,u} then which of the following is a correct statement

If Y={a,e,{I,o} u} then which of the following is a correct statement ?

Which of the following I a correct statement?

If Y={{ a,e},{I,o},u} then which of the following is a corrcet statements ?

Let E = {a,b}, which one of the following statements are correct or incorrect? {a} in E

Three particles have speeds of 2u, 10u and 11u. Which of the following statements is correct ?

In double refraction we get two refracted rays, i.e., O-ray and E-ray. Which one of the following statements is correct?

For the equation (e^-x)/(x+1) which of the following statement(s) is/are correct ?