Question

Given that the atomic radius of silver is `145*"pm"`, how many silver atoms will span a length of `4.70*mm`?

Answer 1

In effect they are asking how many lengths of `290*"pm"` will fit into a length of `4.70*mm`....

Explanation:

Now we can do this dimensionally......

`(4.70xx10^-3*m)/(290xx10^-12*m)=1.621xx10^7` individual silver atoms.....

Why did I double the given radius? Did I make an error?

We note that `1*mm-=1xx10^-3*m`...

And that `1*"picometre"-=1xx10^-12*m`

The rest is arithmetic. Of course, we have to do the ratio properly. I have never found it straightforward.