n-factor of Ca(OH)4 = 4 (because when dissociated, it gives out 4 OH⁻ ions)
Normality=Molarity×n−factor=0.05×2=0.1=N1
Volume of CaOH4 required =V1
Normality of H2PO4 =0.1=N2
Volume of H2PO4 =10ml=V2
Using the formula N1V1=N2V2
(0.1)×(V1)=(0.1)×(10)
V2=10.1
V2=10ml
Thus, 10ml of 0.05M Ca(OH)4 is required to neutralise 10ml of 0.1N H2PO4.