Which of the following is multimolecular colloid?

An element has a bcc structure with cell edge of 288 pm . The density of element is $$7.2 \mathrm{~g} \mathrm{~cm}^{-3}$$. What is the atomic mass of an element?

What is the secondary valence of $$\mathrm{Co}^{3+}$$ ion according to Werner's theory in $$\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4 \mathrm{Cl}_2\right]^{+}$$?

Which of the following elements belongs to first inner transition series?