4. is this equation balanced? explain your answer. na + cl2 → nacl ?

              No, this equation is not balanced.

                    The given equation is as follow,

                                 Na  +  Cl₂    →    NaCl

Element                           LHS                             RHS

Sodium                               1                                   1

Chlorine                             2                                  1

As shown in table, the number of sodium atoms on both left hand side and right hand side are equal and balanced, but, the number of chlorine atoms on left hand side are two while, there is only one chlorine atom on right hand side. Hence, this equation is not following law of conseravtion of mass.

                   The balance chemical equation i as follow,

                                 2 Na  +  Cl₂    →    2 NaCl

Element                           LHS                             RHS

Sodium                               2                                   2

Chlorine                             2                                   2

This equation is obeying law of conservation of mass and the number of each elements are equal on both sides of the equation.

Beryllium, because it is in period 2 and has four total electrons.

Explanation: