Are you sure you copied that down correctly? I know what NH3 is but HJ I am comming up blank on. The only thing HJ I know is hebdojoule which is unit system.
Are you doing chemical balancing?
An example of a monatomic cation would be Cs+. As this is the only cation that consists of a single atom.
Of these options, I'd say the third choice or "Many species of organisms that lived long ago are now extinct". I hope this helps :)
Molarity = Moles/Liter
Use the molecular atomic mass of NaCl to convert from grams to moles.
Molecular mass of NaCl is the sum of its atomic masses. Look at the periodic table to find these. Na is 23 g/mol and Cl is 35.5 g/mol ,
so NaCl = 23 + 35.5 = 58.5 g/mol
multiply to cancel out grams
76 g NaCl * (1mol / 58.5 g NaCl) = 1.3 mol NaCl
over 1 Liter is just 1.3 M NaCl