how to calculate the n factor of a compound

Hello.
There is a different meaning for n factor for acid base and salt,

FOR ACID:
In acid it is number of H+ Ion replaced by one mole of acid in a reaction.
eg:

• n factor of H2SO4:

H2SO4+NaOH------------->NaHSO4+H2O
at a glance H2SO4 has 2 replaceable atoms but in the above reaction only one H+ ion is replaced so it's n-factor is 1.

• n-factor of HCl:

HCl+NaOH------------->NaCl+H2O
In th eabove chical eqn only one H+ ion is replaced so it's n-factor is 1.

FOR BASES:
in bases it is number of OH- Ion replaced by one mole of base in a reaction.
eg:

• n-factor of NaOH:

NaOH+HCl---------------> NaCl+H2O
In the above chemical reaction only one OH- ion is replaced so its n- factor is 1.

• n-factor of NH4(OH):

NH4(OH)+HCl--------------->NH4Cl+H2O
In the above chemical reaction only one OH- ion is replaced so its n- factor is 1.

FOR SALTS:
Inserts it is number of cationic /anionic charge replaced by 1 mole of salt.
OR
Number of moles of electron exchanged ( lost or gained) buy one mole of the salt.
eg:

• n-factor of Na3PO4:

2NaPO4+3BaCl2---------------> 6NaCl+Ba(PO4)2
In the above reaction for having one mole of Ba3(PO4)2 , 2 mole of Na3PO4 is required which means six mole of Na+ are completely replaced by 3 mol of Ba2+.
So six mole of cationic charge is replaced by 2 mole of Na3PO4 Hence n-factor of Na3PO4 in above reaction is 3.
Best of luck.