**(i)** Given,

\( A = \{1,2,\{3,4\},5\}\)

To find if {3, 4} ⊂ A is correct or incorrect.

A set A is said to be a subset of B if every element of A is also an element of B

A⊂ B if a ∈ A,a ∈ B

From the above statement,

3 ∈ {3, 4}; however 3∉A

The given statement {3, 4} ⊂ A is incorrect.

**(ii)** Given that,

\( A = \{1,2,\{3,4\},5\}\)

To find if {3, 4} ∈A is correct or incorrect.

From the above statement,

{3, 4} is an element of A.

{3, 4} ∈A

The given statement is correct.

**(iii) **Given that,

\( A = \{1,2,\{3,4\},5\}\)

To find if {{3, 4}} ⊂ is correct or incorrect.

A set A is said to be a subset of B if every element of A is also an element of B

A⊂ B if a ∈ A,a ∈ B

From the above statement,

{3, 4} ∈ {{3, 4}} and {3, 4} ∈ A

{{3, 4}} ⊂ A

The given statement {{3, 4}} ⊂ A is correct.

**(iv) **Given that,

\( A = \{1,2,\{3,4\},5\}\)

To find if 1∈ A is correct or incorrect.

From the above statement,

1 is an element of A.

The statement 1∈A is a correct statement.

**(v) **** **Given that,

\( A = \{1,2,\{3,4\},5\}\)

To find if 1⊂ A is correct or incorrect.

A set A is said to be a subset of B if every element of A is also an element of B

A⊂ B if a ∈ A,a ∈ B

From the above statement,

An element of a set can never be a subset of itself. So \( 1\nsubseteq A\)

The given statement 1⊂ A is incorrect statement.

Find the symmetric difference A Δ B, when A = {1, 2, 3} and B = {3, 4, 5}.