Statement - I : (A) Decomposition of Ammonia on platinum surface at high pressure is a zero order reaction
Statement - II : (R) At high pressure, metal surface gets saturated with gas molecules

Decomposition of a gas on metal surface at high pressure is zero order reaction and low pressure it is first order reaction.

Number of adsorption sites are limited,all the sites on a metal surface are occupied by the gas molecules when the gas pressure is high.The product molecules are less strongly adsorbed than the reactant molecules. As soon as the product molecules escapes from the sites the waiting reactant molecules are adsorbed making the concentration of reactants on the surface constant and rate of reaction remains constant

At low pressures all the adsorption sites  are not occupied.