The atomic number of fluorine is 9. How many electrons does an ion of fluorine have if it is represented by the symbol shown below? 19F1-

A. 8 electrons
B. 9 electrons
C. 10 electrons
D. 20 electrons

Hence it has taken 1 electron

Now first look at EC of Fluorine(F)

Look at the EC

Or

Option C is correct.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.