{HEAD ~ The aqueous solution} of sodium hydroxide, which is {TAIL ~ the heavier phase}, contains most of the catalyst 
is
{ HEAD ~ The aqueous solution } of sodium hydroxide , which is { TAIL ~ the heavier phase } , contains most of the catalyst
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH