pH of solution made by mixing 100 mL of 0.2 M Ca(OH)₂ and 0.1 M NaOH each

Milli moles of OH^– from Ca(OH)₂ = 100 × 0.2 × 2 = 2 × 20 = 40
Milli moles of OH^– from NaOH = 100 × 0.1 = 10
Total milli moles of OH^– = 40 + 10 = 50
Total volume in ml = 100 + 100 = 200 ml
Molarity of OH^– $=\frac{50}{200}=0.25\mathrm{M}$
pOH = – log (0.25) = 0.6
pH = 14 – 0.6 = 13.4