7. Which of the following substances contains two pi bonds? (A) C₂H₄ (B) C₃H₈ (C) C₂H₂ (D) C₂H₆ (E) CH₄

17. Which of these is an isoelectronic series? (A) $\text{Na}^+$, $\text{K}^+$, $\text{Rb}^+$, $\text{Cs}^+$ (B) $\text{K}^+$, $\text{Ca}^{2+}$, $\text{Ar}$, $\text{S}^{2-}$ (C) $\text{Na}^+$, $\text{Mg}^{2+}$, $\text{S}^{2-}$, $\text{Cl}^-$ (D) $\text{Li}$, $\text{Be}$, $\text{B}$, $\text{C}$ (E) None of these (A-D)