Let us evaluate all the statements:

1. The concentration of pure liquid water, $H_2O(l)$, is constant (approx. 55.5 M) and its active mass is taken as unity. It will not be equal to the concentration of $CO_2(g)$. Hence, this statement is true.
2. The equilibrium constant $K_p$ is expressed in terms of partial pressures, not molar concentrations. Also, the stoichiometric coefficient of $O_2$ is 2, so it should be squared. The correct expression is $K_p = \frac{p_{CO_2}}{p_{CH_4} \cdot p_{O_2}^2}$. Similarly, $K_c = \frac{[CO_2]}{[CH_4][O_2]^2}$. The expression given in the option misses the square on $O_2$ and uses concentration brackets for $K_p$. Thus, this statement is not true.
3. According to Le Chatelier's principle, adding reactants ($CH_4$ or $O_2$) to a system at equilibrium will shift the equilibrium in the forward direction (to the right) to consume the added reactants. Thus, this statement is true.
4. The enthalpy change of the reaction, $\Delta_r H$, is negative ($-170 \text{ kJ mol}^{-1}$), which indicates that heat is released. Thus, the reaction is exothermic. This statement is true.