Answer
$$ 1.228 \space JK^{-1}g^{-1}$$
Work Step by Step
1. Determine the molar mass of sodium $\big(Na\big)$
According to the periodic table, the molar mass of $Na$ is: $22.99 \space g/mol$
2. Divide the molar heat capacity of sodium by its molar mass, in order to calculate its specific heat capacity:
$$C_s = \frac{C_m}{molar \space mass} = \frac{28.24 \space JK^{-1} mol^{-1}}{22.99 \space g/mol} = 1.228 \space JK^{-1}g^{-1}$$
