I think.....mgmat tests are way tougher than the gmat prep tests...especially questions from probability and modulus are quite tough.....gmat prep is a better way to judge ur performance....

The first is true coxz the diagonals are perpendicular bisectors


the second seems true as all sides are equal (though at first instinct ul feel it duc b a square also, but square is a special kind of rhombus)

Thats the only feasible explanation accordin to me....

hope im rite!