Which ionization process requires the most energy?

Explain the variation in the ionization energies of carbon, as displayed in this graph:

At 50 °C, the ion-product constant for H2O has the value Kw = 5.48 * 10-14. (a) What is the pH of pure water at 50 °C? (b) Based on the change in Kw with temperature, predict whether ΔH is positive, negative, or zero for the autoionization reaction of water: 2 H2O1l2 Δ H3O+1aq2 + OH-1aq2

The K_w for water at 0°C is 0.12×10⁻¹⁴. Calculate the pH of a neutral aqueous solution at 0°C.