Respuesta :

Willchemistry
Molar mass NaOH = 40.0 g/mol

number of moles : 8.4 / 40.0 => 0.21 moles

1 mole ---------------- 6.02 x 10²³ molecules
0.21 moles ---------- ?

molecules :  ( 0.21 ) x  ( 6.02 x 10²³ ) / 1

= 1.264 x 10²³ molecules

hope this helps!