Which from following is NOT true about natural rubber?

Identify the element having smallest ionic size in +3 state from following.

Which from following is NOT a dicarboxylic acid?

Calculate the volume of unit cell of an element having molar mass $63.5 \mathrm{~g} \mathrm{~mol}^{-1}$ that forms fcc structure $\left[\varrho \times \mathrm{N}_{\mathrm{A}}=5.5 \times 10^{24} \mathrm{~g} \mathrm{~cm}^{-3} \mathrm{~mol}^{-1}\right]$