Which of the following elements exhibits negative oxidation state ?

IV A group elements
Common oxidation state is : "+4"
C shows :- +4 -4
Si:- +4 [Stable]

$$\begin{gathered} \mathrm{Ge}, \mathrm{Sn}\left.\begin{array}{r} \\ \end{array}\right\}- +2,\underset{\mathrm{stable}}{+4} \\ \mathrm{Pb}: - \underset{\mathrm{stable}}{+2}, +4 \end{gathered}$$
→ For Ge,Sn +4 is stable oxidation state hence in +2 oxidation state they acts as reducing agents
→ Where as for Pb +2 oxidation state is stable [due to inert pair effect] hence in +4 oxidation state Pb acts as oxidising agent
→ Higher oxidation state is due to involvement of ns and np electrons
i.e., 

Lower oxidation state is due to involvent of only np electron
i.e., ns² np⁽²⁾ ⇒ +2
Higher oxidation stable stability dcecreases from top to bottom

$$\begin{gathered} {\mathrm{Ge}}^{+4}>{\mathrm{Sn}}^{+4}>{\mathrm{Pb}}^{+4}\left[\mathrm{Stability} \mathrm{order}\right] \\ {\mathrm{Ge}}^{+4}<{\mathrm{Sn}}^{+4}<{\mathrm{Pb}}^{+4}\left[\mathrm{Oxidising} \mathrm{power} \mathrm{order}\right] \end{gathered}$$
Lower oxidation state  stability increases from top to bottom
Ge⁺² < Sn⁺² < Pb⁺² : Stability order
Eg : 

Be₂C ⇒ C^-4
Al₄C₃ ⇒ 4Al⁺³  3C^-4