Which from following compounds is NOT in solid state at $25^{\circ} \mathrm{C}$ ?

Calculate the molar mass of solute when 4 g of it dissolved in $1 \mathrm{dm}^3$ solvent has osmotic pressure 2 atm at 300 K . [R $\left[=0.082 \mathrm{~dm}^3 \mathrm{~atm} \mathrm{~K} \mathrm{~mol}^{-1}\right]$

Identify thermoplastic polymer from following.

Calculate radius of fourth orbit of $\mathrm{B}^{4+}$ ion.