Numbering starts from the leftmost figure.
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1) Opposite sides are equal $\implies$ quadrilateral is a parallelogram. (Can be proven using basic congruency theorems)
2)
Opposite sides are parallel $\implies$ trapezium.
But the other pair of sides are not parallel, hence in the general case this is not a parallelogram but is a trapezium with two equal sides.
3) One pair of opposite sides are congruent and parallel $\implies$ this is a parallelogram.
Proof: Join two vertices and you get that the two triangles formed are congruent.
4)
Diagonals are bisected at their intersections $\implies$ Quadrilateral is a parallelogram.
Show that the two opposite little triangles are congruent by using SAS test (or whatever you call it)
So the figure which is not a parallelogram is 2.
