If a penny is made of 3.11 grams of copper, how many atoms of copper are in the penny

2.94x10²² atoms of Cu

Explanation:

We must work with NA to solve this, where NA is the number of Avogadro, number of particles of 1 mol of anything.

Molar mass Cu = 63.55 g/mol

Mass / Molar mass = Mol → 3.11 g / 63.55 g/m = 0.0489 moles

1 mol  of Cu has 6.02x10²³ atoms of Cu

0.0489 moles of Cu, will have (0.0489  .NA)/ 1 = 2.94x10²² atoms of Cu

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.