Answer:
[tex]\boxed {\boxed {\sf B. \ 1.5 *10^{23} \ formula \ units}}[/tex]
Explanation:
1 mole of any substance contains the same number of particles. The particles can vary (atoms, molecules, formula units), but there are always 6.022*10²³ particles. In this case, the particles are formula units of potassium nitrate or KNO₃.
Let's create a ratio.
[tex]\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}[/tex]
Since we are trying to find the formula units in 0.250 moles, we multiply by that number.
[tex]0.250 \ mol \ KNO_3 *\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}[/tex]
The units of moles of potassium nitrate cancel.
[tex]0.250 *\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 }[/tex]
The denominator of 1 can be ignored, so we can make a simple multiplication problem.
[tex]0.250 *{6.022*10^{23} \ formula \ units \ KNO_3}[/tex]
[tex]1.5055 * 10^{23} \ formula \ units \ KNO_3[/tex]
If we round to the nearest tenth, the 0 in the hundredth place tells us to leave the 5 in the tenth place.
[tex]1.5 *10^{23} \ formula \ units \ KNO_3[/tex]
0.250 moles of potassium nitrate is approximately equal to 1.5*10²³ formula units of potassium nitrate and choice B is correct.
