Answer:
0.97 × 10⁹ strontium atoms
Explanation:
if 1 pm is equal with 10⁻⁹ mm
then 215 pm are equal to X mm
X = (215 × 10⁻⁹) / 1 = 215 × 10⁻⁹ mm
Now the diameter of the strontium atom is twice the radius:
diameter = 215 × 10⁻⁹ × 2 = 430 × 10⁻⁹ mm
if 1 strontium atom have a diameter of 430 × 10⁻⁹ mm
then X strontium atom are needed to be laid said by side to span a distance of 419 mm
X = (419 × 1) / (430 × 10⁻⁹) mm = 0.97 × 10⁹ strontium atoms
