Assertion: Combustion of all organic compounds is an exothermic reaction.

Reason: The enthalpies of all elements in their standard state are zero.

1.  Both assertion and reason are true and the reason is the correct explanation of assertion.

2.  Both assertion and reason are true and the reason is not the correct explanation of assertion.

3.  Assertion is true but the reason is false.

4.  Assertion is false but the reason is true.

On the basis of thermochemical equations (1), (2), and (3), find out which of the algebraic relationships given in options (a) to (d) is correct

(i) $\mathrm{C} \left(\mathrm{graphite}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right); {∆}_{\mathrm{r}}\mathrm{H}=\mathrm{x} \mathrm{kJ} {\mathrm{mol}}^{-1}$

(ii) $\mathrm{C} \left(\mathrm{graphite}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to \mathrm{CO}\left(\mathrm{g}\right); {∆}_{\mathrm{r}}\mathrm{H}=\mathrm{y} \mathrm{kJ} {\mathrm{mol}}^{-1}$

(iii) $\mathrm{CO}\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right); {∆}_{\mathrm{r}}\mathrm{H}=\mathrm{z} \mathrm{kJ} {\mathrm{mol}}^{-1}$

1. z=x+y

2. x=y-z

3. x=y+z

4. y=2z-x

The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound is -

1. Generally negative

2. Always positive

3. Zero

4. Never negative

The enthalpy of sublimation of a substance is equal to -

1. Enthalpy of fusion + Enthalpy of vaporisation

2. Enthalpy of fusion

3. Enthalpy of vaporisation

4.  Twice the enthalpy of vaporisation