A decrease in the amount of gas in a container will mean a decrease in pressure.
The length of time required for half of the radioactive atoms in a sample to decay is its <span>half-life. The correct option among all the options that are given in the question is the first option or option "A". The other choices are incorrect and can be easily neglected. I hope that this is the answer that has come to your help.</span>
Answer : The enthalpy of the given reaction will be, -1048.6 kJ
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
The main reaction is:

The intermediate balanced chemical reactions are:
(1)

(2)

(3)

(4)

(5)

Now reversing reaction 2, multiplying reaction 3 by 4, reversing reaction 1 and multiplying by 2, reversing reaction 5 and multiplying by 2 and then adding all the equations, we get :
(1)

(2)

(3)

(4)

(5)

The expression for enthalpy of main reaction will be:



Therefore, the enthalpy of the given reaction will be, -1048.6 kJ
Water
Water is a compound because it is made from more than one kind of element (oxygen and hydrogen).