Which is true of hydroxide ions
a- they contain two hydrogen atoms
b- they dissociate to form protons
c- they have a negative charge
d- they are not found in pure water

Option (C) is the correct answer.

Explanation:

A hydroxide ion is an ion that has -1 charge and contains an oxygen and hydrogen atom together.

So, basically a hydroxide ion is ion.

Where as a hydrogen ion is defined as the ion in which a hydrogen atom holds a positive charge, that is, .

A proton is a sub-particle present inside the nucleus of an atom and it holds a positive charge. Symbol of proton is .

Thus, we can conclude that the statement they have a negative charge, is true of hydroxide ions.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.