The number of transferred electrons to form the ionic bond in one formula unit of each compound is as below
NaCl = 1 electron
CaS = 2 electrons
BaO= 2 electrons
KBr=1 electrons
LIF = 1 electron
Step-by-step explanation
ionic bond is formed between a metal and a nonmetal . This bond is formed when electron are transferred between cation and anion. To know how many electrons transferred you look the oxidation state of the metal.
for example
in NaCl only one electrons is transferred since Na is in oxidation state of +1. Na donate the one electron to Cl to form an ionic bond. Ba is in oxidation state of 2+ and hence it donate the two electrons to O to form ionic bond.