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Commercially, it is used as fuel, as a reducing agent and in the manufacture of metal hydrides., , Hydrides, , There are three types of hydrides — ionic or salt-like hydrides, covalent or molecular hydrides and, metallic or non-stoichiometric hydrides., , lonic or salt-like hydrides are binary compounds of hydrogen with s block elements, which are, highly electropositive in nature., , Covalent or molecular hydrides are binary compounds of hydrogen with more electro-negative, elements, such as p block elements., , Covalent hydrides are further divided into electron-deficient hydrides, electron-precise hydrides, and electron-rich hydrides., , Metallic hydrides are binary compounds of hydrogen with d and f block elements., , Except for chromium from group 6, the metals of groups 6, 7, 8 and 9 do not form hydrides. The, inability of these metals to form hydrides is called the hydride gap of d block., , Water and its Properties, , Water is a tasteless and odourless liquid at standard temperature and pressure., , Water has strong hydrogen bonding in between molecules, and, therefore exists as associated, molecules., , Due to the presence of extensive hydrogen bonding in between molecules, water has high freezing, point, boiling point, heat of vaporisation and heat of fusion. It has high thermal conductivity,, surface tension, dipole moment, dielectric constant and highest specific heat.