Amonium or Ammonium: How To spell?
The word Amonium is misspelled against Ammonium, a noun meaning "A compound radical, NH4, having the chemical relations of a strongly basic element like the alkali metals."
Ammonium has double "mm" is mispronounced as "m"Remember double 'MM' in between the strings a & onium which should not be misspelled with single 'M'
Wrong Spelling:  a-m-onium  Correct Spelling:  a-mm-onium 
Check more misspelled words of Ammonium to spell it correct.