Question

An isotope of an element with a relative atomic mass of 19 amu and 10 neutrons has a charge of 1-. How many electrons does it have?

Answer 1

amu= proton + neutron
19= proton + 10
proton=9
--------------------------------
We know that proton = electron
Electron =9
But it has an extra charge of -1,
so,
Electron =10

Answer 2

\[^A_Z\text E^{q}_N\]
\[A=Z+N\]\[Z=e+q\]

\[^{19}_Z\text E^{-1}_{10}\]
\[19=Z+10\qquad\rightarrow Z=19-10\]\[Z=e-1\qquad\rightarrow e=Z+1\]