What do the solid wedge and dashed wedge symbols indicate in the 3D representation of an organic molecule?

An organic compound $C_3H_6O$ does not give a precipitate with $2,4-$Dinitrophenylhydrazine reagent and does not react with metallic sodium. The compound is:

Given below are two statements:
Statement-$I$ : Compound $(X)$, shown below, dissolves in $NaHCO_3$ solution and has two chiral carbon atoms.
Statement-$II$ : Compound $(Y)$, shown below, has two carbons with $sp^3$ hybridization, one carbon with $sp^2$ and one carbon with $sp$ hybridization.
In the light of the above statements, choose the correct answer from the options given below:

Match List-$I$ with List-$II$.
| List-$I$ | List-$II$ |
| :--- | :--- |
| $(A)$ Tetrahydrofuran | $(I)$ Spiro compound |
| $(B)$ Bicyclo[$1.1$.$0$]butane derivative | $(II)$ Aromatic compound |
| $(C)$ Spiro[$2.2$]pentane derivative | $(III)$ Non-planar heterocyclic compound |
| $(D)$ Furan | $(IV)$ Bicyclo compound |
Choose the correct answer from the options given below.

Which one of the following formulae does not represent an organic compound?

The number of secondary carbon atoms present in the following compounds are respectively: