​Common salt obtained from sea - water contains 8.755 % NaCl by mass . The no. of formula units of NaCl present in 25 g of this salt is :
a) 3.367 * 1023 formula units
b) 2.258 * 1022 formula units
c) 3.176 * 1023 formula units
​d) 4.73 * 1025 ​formula units

8.775 % by mass means 8.775 g of NaCl is present in 100 g sampleSo 25 g of the sample contains          = 8.775100 × 25         = 2.193 g of NaCl58.5 g of NaCl = Molecular mass = Avogadro no of particles = 6.022 × 1023 of NaCl unit cell2.193 g of NaCl contains = 2.19358.5  × 6.023 × 1023         = 2.258 × 1022 NaCl units

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