Which of the following are examples of the null set

Set of odd natural numbers divisible by $2$

Consider the sets

$\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$

Insert the symbol $\subset$ or $ \not\subset $ between each of the following pair of sets:

$B \ldots \cdot C$

Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 2 \, ....... \, A $

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

$1 \subset A$

If $A$ and $B$ are any two non empty sets and $A$ is proper subset of $B$. If $n(A) = 4$, then minimum possible value of $n(A \Delta B)$ is (where $\Delta$ denotes symmetric difference of set $A$ and set $B$)

Write the following sets in roster form :

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