Two diagonals are not necessarily equal in a/an?
rhombus
Explanation for correct option
The rhombus is a quadrilateral having all sides are equal and the opposite sides are parallel.
The diagonal of rhombus bisects each other at and the length of both diagonals need not to be equal.
Explanation for incorrect option
We know that the diagonal of a rectangle, square and isosceles trapezium are always equal.
Hence, the correct option is B