Pure platinum is very malleable. We add different metals to platinum to harden the platinum. Iridium is added to add even further toughness. Iridium is more expensive than ruthenium. Iridium is harder than ruthenium.
White gold is an alloy of gold and some white metals such as nickel, silver and palladium.
White gold can be 18k, 14k, 9k or any karat. Platinum is not susceptible to problems like stress corrosion or stress cracking as can be the case with white gold. No special care is required in handling platinum jewelry. Soaking platinum in a mild solution of soap and warm water and gently rubbing it with a soft-bristled brush is usually all that is required to maintain platinum's luster.