Is it possible to identify something as an element, compound or pure substance

The alkali metals (group 1) consist of lithium (3), sodium (11), potassium (19), rubidium (37), cesium (55), and francium (87). they are soft, metallic solids with low densities and low melting points. based on the data shown in figure 1, how many valence electrons do alkali metals share?

Which metal exist in liquid state and can be cut with knife ?

What is the molar mass of a gas that has density of 2.054 g/l