Which of the following is an endothermic reaction?

The heat of neutralisation of $NaOH$ and $HCl$ is $-57.46 \, kJ/eq$. What is the heat of ionisation of water in $kJ/mol$?

The combustion enthalpies of carbon,hydrogen,and methane are $-393.5 \ kJ/mole$,$-284.8 \ kJ/mole$,and $-890.4 \ kJ/mole$ respectively at $25 \ ^oC$. The value of the standard formation enthalpy of methane at that temperature is ..... $kJ/mole$.

Fill in the blanks:
$(i)$ The enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states is called the ....... of that compound.
$(ii)$ The total heat change in a chemical reaction is equal to the algebraic sum of the heat changes of the individual steps of the reaction. This law was given by .......... .
$(iii)$ $A$ process during which there is no exchange of heat between the system and the surroundings is called an ........... process.

When $1 \, \text{mol}$ of anhydrous salt $AB$ is dissolved in water,$21.0 \, J \, \text{mol}^{-1}$ of heat is released. The enthalpy of hydration of $AB$ is $-29.4 \, J \, \text{mol}^{-1}$. What is the enthalpy of solution of the hydrated salt $AB \cdot 2H_2O_{(s)}$ in $J \, \text{mol}^{-1}$ (in $.4$)?

What is the enthalpy change for $2H_2O_{2(l)} \to 2H_2O_{(l)} + O_{2(g)}$ if the heats of formation of $H_2O_{2(l)}$ and $H_2O_{(l)}$ are $-188 \ kJ/mol$ and $-286 \ kJ/mol$ respectively?