The answer is; A
The force or weight and distance on both sides of the fulcrum is given by the following ratio;
MA = Fb/Fa = a/b (MA = Mechanical Advantage)
The greater the distance from the fulcrum on which force is applied to lift a load on the other side of the fulcrum, the less the effort required.
Atomic number is your answer.
<span>Na (sodium) is highly electropositive. Its has 1 electron in its outermost orbit which is transferred to an electronegative atom to form an ionic bond.
It only needs to get rid of one valence electron to take part in a reaction. That's how it's highly reactive.</span>