The stefan-boltzmann law can be employed to estimate the rate of radiation of energy h from a surface, as in 4 (m'), the emissivity h aeot where h is in watts, a = the surface area that characterizes the emitting properties of the surface (dimensionless), o 5.67 x 10 wm k), andt е a universal constant -8 -2 absolute temperature = 0.90, and t= 650 20 k called the stefan-boltzmann constant (k).

Answer:             1.0  × 10⁻⁵ msolution:                     as we know ph is given as,                                    ph  = -log [h⁺]and,                                    [h⁺]  =  10^-ph    (1)putting value of ph in eq. 1,                                    [h⁺]  =  10⁻⁵                                    [h⁺]  =  1.0  × 10⁻⁵ m