How many water molecules will be generated when single nucleotides are used to make this RNA: 5’-UUAACCGUCAG-3’?
It's one for every phosphodiester bond formed. 11 nucleotides, but only 10 bonds needed to join them into an oligonucleotide:

1  2  3  4  5  6  7  8  9  10 11
N--N--N--N--N--N--N--N--N--N--N
 1  2  3  4  5  6  7  8  9  10