Answer:
To calculate the number of moles of HCl in the solution, we can use the formula:
moles = concentration x volume
where concentration is in units of moles per liter (M), and volume is in units of liters (L).
Converting the given volume to liters:
266 mL = 266/1000 L = 0.266 L
Substituting the given values into the formula:
moles = 0.260 M x 0.266 L
moles = 0.06896 mol
Therefore, the number of moles of HCl in the solution is 0.06896 mol (rounded to five significant figures).