JEE Advanced levelSingle correct optionDifficulty 3 of 3cc044
Three isomers of formula CrClX3⋅6HX2O differ in how many chloride ions are free. In the isomer which on treatment of one mole with excess AgNOX3 gives two moles of AgCl immediately, the number of water molecules directly coordinated to chromium (coordination number 6) is
A6
B3
C5
D4
Answer: C
Two free chlorides mean one chloride is bound. With coordination number 6 and one ClX− inside, five HX2O are coordinated. The formula is [Cr(HX2O)X5Cl]ClX2⋅HX2O, whose sixth water is lattice water.