As the temperature is increased or pH is increased, the rate rises till it is maximum at 37°C (physiological temperature) or pH = 7·4 and then falls off, as shown in the adjoining

(i) Physical adsorption is an exothermic process in equilibrium
Gas (Adsorbate) + Solid (Adsorbent) \(\rightleftharpoons \) Gas absorbed on Solid + Heat
As the temperature is increased, by Le Chatelier's principle, equilibrium shifts in the backward direction, i.e., adsorption  decreases
(ii) Brownian movement is due to bombardment of colloidal particles by the molecules of the dispersion medium with unequal forces from different directions. As a result, there is a resultant force acting on it causing the particle to move.
(iii) This is due to the diserable size of the colloidal particles (\(10\mathring { A } -10000\mathring { A } \)) .

SnO₂ reacts with a base, e.g., NaOH to form sodium stannate (Na₂SnO₃) in the solution. The stannate ions are adsorbed on the surface of SnO₂ particles giving them a negative charge.
\({ SnO }_{ 2 }+2\quad NaOH\longrightarrow { Na }_{ 2 }{ SnO }_{ 3 }+{ H }_{ 2 }O\)
                                         sodium stanne
\(\\ { SnO }_{ 2 }+{ SnO }_{ 3 }^{ 2- }\quad \longrightarrow [{ SnO }_{ 2 }]:{ SnO }_{ 3 }^{ 2- }\)
                                          negatively charged colloidal particles

\(CH=CH+{ H }_{ 2 }\underrightarrow { Pd } { CH }_{ 2 }={ CH }_{ 2 }\overset { { +H }_{ 2 } }{ \underset { Pd }{ \rightarrow } } { CH }_{ 3 }\_ { CH }_{ 3 }\)
\(\\ \quad \quad Acetylene\quad \quad \quad \quad \quad \quad Ethane\quad Ethane\)
\(\\ CH=CH+{ H }_{ 2 }\overset { Pd+Ba{ SO }_{ 4 } }{ \underset { +quinoline/S }{ \longrightarrow } } { CH }_{ 2 }={ CH }_{ 2 }\)
                                                Ethane
BaSO₄ + quinoline/S poison the catalyst. Hence, the efficiency of the catalyst decreases and the reaction stops at the first stage of reduction.

At the time of setting, the sun is at the horizon. The light emitted by the sun has to travel a longer distance through the atmosphere. As a result, blue part of the light is scattered away by the dust particles in the atmosphere. Hence, the red part is visible.