The electronegativity of the given elements increases in the order

Since electronegativities increase in a period from left to right, therefore, electronegativity of $\mathrm{N}$ is more than that $\mathrm{C}$ and electronegativity of $\mathrm{P}$ is more than that of $\mathrm{Si}$. Further since electronegativities decrease down a group in the periodic table, therefore, electronegativity of $\mathrm{C}$ is more than that of $\mathrm{Si}$ and electronegativity of $\mathrm{N}$ is more than that of $\mathrm{P}$. Hence, the electronegativity of the given elements increases in the order $\mathrm{Si},\mathrm{P},\mathrm{C},\mathrm{N}$.