Answer:  Second diagram and fourth diagram.

Step-by-step explanation:

A kite is a quadrilateral which has two pairs of congruent adjacent sides.

In diagram 1:

By the distance formula,

The sides of the given quadrilateral are sqrt{a^2+c^2},  sqrt{b^2+c^2}, sqrt{b^2+d^2} and sqrt{a^2+d^2}

Since, here a, b, c and d are unknown numbers,

Thus, this quadrilateral does not have any pair of congruent adjacent sides.

It is not a kite.

In diagram 2:

By the distance formula,

The sides of the given quadrilateral are a,  asqrt{5}, asqrt{5} and a

Since, this quadrilateral has two pairs of congruent adjacent sides.

It is a kite.

In diagram 3:

By the distance formula,

The sides of the given quadrilateral are a,  sqrt{b^2+(c-a)^2}, sqrt{(b-a)^2+c^2} and a

Since, here a, b, c and d are unknown numbers,

Thus, this quadrilateral only have only one pair of congruent adjacent sides.

It is not a kite.

In diagram 4:

By the distance formula,

The sides of the given quadrilateral are sqrt{b^2+c^2},  sqrt{b^2+c^2}, sqrt{a^2+c^2} and sqrt{a^2+c^2}

Since, this quadrilateral has two pairs of congruent adjacent sides.

It is a kite.