Bunuel wrote:
Is rectangle ABCD a square?
(1) Angle ABC = 90
(2) AC is prependicular of BD
St.1 says that AB or BC are not diagonals. Further, we can make out that AC and BD are diagonals.
But all rectangles are not square. Therefore,
Insufficient
St.2 All squares are rectangles but all rectangles are not squares. A rectangle is also a square when the diagonals of the rectangle intersect each other at right angles (remember both diagonals of a rectangle are deemed to be congruent. So we don't need to prove this property of a square). This option says this.
Now here is the tricky part.
I am tempted to pick B for this as from the stem it is obvious that all the angles of ABCD are right. St 1 states something redundant (I agree with
14101992 on this one). The only thing that St 1 establishes (by a stretch of imagination) is the order of the points on the rectangle. But we can even make out from St 2 that AC and BD are perpendicular, for on a rectangle 2 sides, which are perpendicular, will be adjacent and will have a point common.