Answer to Question 1
Productivity refers to the amount of goods and services produced per worker. Per capita real GDP increases only if productivity increases, so, increases in a country's standard of living are tied to increases in productivity.
Answer to Question 2
Most economists believe that even though employers and employees each pay half of the FICA tax, the burden of the tax falls almost entirely on employees. The forces of demand and supply working in the labor market determine the incidence of the tax, not Congress, so even though the tax is paid evenly by employers and employees, this does not mean that the burden is shared equally.