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Ricky18-      Molar mass of any compound is its exact molecular weight (computed from summing up of atomic weights together) in the mass unit of grams.
The molar mass is generally expressed in grams or gram/mol
To calculate the molar mass of NaOH, first you need to know about the molecular weight of the NaOH. to be able to do that , first find the atomic weight of the Na, O, and H from the periodic table.

Atomic weight of Na 22.98976928,
Hydrogen’s standard atomic weight is 1
oxygen has a standard atomic weight of 15.9994.

Add the atomic weight of all 3 which will be 39.9892

So, the molar mass of NaOH is 39.9892 gm/mol.
Na+O+H= 23+16+1=40amu