Write the following sets in roster form :
$B = \{ x:x$ is a natural number less than ${\rm{ }}6\} $
Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?
$\{\varnothing\} \subset A$
State whether each of the following set is finite or infinite :
The set of letters in the English alphabet
Which of the following sets are finite or infinite.
$\{1,2,3 \ldots .\}$
How many elements has $P(A),$ if $A=\varnothing ?$