find the number of ions in one litre of solution which contain water and 9.75 gram of NaCl

Dear Student,

According to question,
Moles of NaCl = 9.75 / 58.44 g/mol =  0.169 mol
1 L of solution cantain = 0.169 moles
​​​​​​​One NaCl ionized Na+ and Cl- so that produce 2 ions
Total ion mole in 1 L = 2 x 0.169 mol
Number of iron in 1 L = 2 x 0.169 x 6.023 x 10²³
Number of iron in 1 L = 2.035 x 10²³ 

Regards