The given elements put into an equation using their symbols are as follows:
Pb +

=

+ Ag
Since there are 2 Pb on the right side of the equation, you would change the coefficient of Pb on the left side to 2:
2Pb +

=

+ Ag
Since there are 2 Acetate on the right side of the equation, you would change the coefficient of Silver Acetate on the left side to 2:
2Pb +

=

+ Ag
Now there are 2 Silver on the left side, so you change the coefficient of Silver on the right side to 2:
2Pb +

=

+ 2Ag
That is your final equation
The coefficients are 2 + 2 = 1 + 2
Answer:
Explanation:
A is Magnesium, B is Aluminium both are adjacent element and lie in third period.
Magnesium with atomic number of 12 consist two s electrons in it's valence shell in ground state whereas, Aluminium which has atomic number of 13 consist three electrons in it's valence shell in the ground state out of which two are s electrons and only one p electron.