The number of elements in the set $\{ (a,\,b):2{a^2} + 3{b^2} = 35,\;a,\,b \in Z\} $, where $Z$ is the set of all integers, is

State which of the following sets are finite or infinite :

$\{ x:x \in N$ and $x$ is prime $\} $

Which of the following are examples of the null set

Set of odd natural numbers divisible by $2$

Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?

$\{ 3,4\}  \in A$

Write the following sets in roster form :

$D = \{ x:x$ is a prime number which is divisor of $60\} $