The radius of a strontium atom is 215 pm. how many strontium atoms would have to be laid side by side to span a distance of 4.19 mm?

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