i am confused about standard enthalphy. may i know which of them that i should put negative sign? They are standard enthalphy of fusion,vaporization and sublimation. Please help me...

Standard enthalpy simply put is heat of reaction released when a certain reactants proceed to products.In vaporization it is negative since liquid is converted to gas which has more energy than the liquid,and sublimation it is positive since solid is formed from liquid like dew.Fusion it is also positive because a new substance is formed and heat is released.

Enthalpy is also constant per molecule of products formed as well as reactants consumed.