How many cyclic structures are possible for $C_4H_6$?

Binomial nomenclature means

$A$ sulphide ore is first converted into its oxide before reduction. This is done because

Two rods of different materials having coefficients of linear expansion $\alpha_1$ and $\alpha_2$ and Young's moduli $Y_1$ and $Y_2$ respectively are fixed between two rigid massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of rods. If $\alpha_1 : \alpha_2 = 2 : 3$,the thermal stress developed in the two rods is equal provided $Y_1 : Y_2$ is equal to:

If $\log (1+x) - \frac{2x}{2+x}$ is increasing,then

The colour of light absorbed by an aqueous solution of $CuSO_4$ is