Gram molar masses of elements:
Sodium: 23g/mol
Hydrogen(molecule): 2g/mol
Oxygen (molecule): 32g/mol
Formula of sodium hydroxide : NaOH
Hence mass of 1 mole of NaOH is :
1 x 23 + 1 x 16 + 1 x 1 = 40g
Therefore the mass of 0.25 moles of NaOH : 0.25 x 40g = 10g
Cheers!
