# Which of the following statements isincorrectregarding water of crystallisation? A)It can be removed by sufficient heat. B)It is in chemical combination with a crystal. C)It is necessary for the maintenance of crystalline properties of the crystal. D)Number of water of crystallization for a given compound depends on the temperature and pressure conditions. In this question it is given the correct answer is "d" but if we take the example of Fe2O3 it contains xH2O it is because of the pressure conditions and temprature right ? and the water of crystalization just exists along with the element and not chemically combined

D)  is incorrect because the number of water of crystallisation of a molecule is decided by the geometry of the molecule. It does not depend on pressure and temperature. In case of Fe2O3.x H2O the value of x does not depend on temperature and pressure. It is dependent on the availability of oxygen for rusting reaction.
The rusting of iron is an electrochemical process. It involves the transfer of electrons from iron to oxygen. Here, iron gives up electron thus acts as reducing agent while oxygen behaves as oxidising agent as it gain electrons.
Reaction can be written as:
O24e -2H2O4OH-
Fe$\to$Fe2 +2e-
Following reactions also occurs:
4Fe2+O2   4Fe3 +2O2-
Fe2 ++2H2O Fe(OH) 2+2H+
Fe3 3H2O    Fe(OH)3+ 3H +
Dehydration equation:

Fe(OH)   FeO + H2O
Fe(OH) 3    FeO(OH)+H2O
2FeO(OH) Fe2O + H2O
Thus we can see that, corrosion products are governed by the availability of water and oxygen. When oxygen is limited, iron (II) containing compounds are formed like FeO and Fe3O4
But when high oxygen is available, then iron(III) compounds are favoured with the formula Fe(OH) 3 -x O x/2.  Thus the value of x is not defined for the formula of rust as it depends on the oxygen available. ​

Water of crystallisation are chemically bonded with the molecule. It include coordinate bonding and hydrogen bonding.

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d is correct

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acc to me B is incorrect

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