Sodium metal is so soft that it can be easily cut with a knife.

Take a piece of iron (or copper) metal. Try to cut it with a knife. We will find that the piece of iron (or copper) metal cannot be cut. Now, hold a piece of sodium metal carefully with a pair of tongs and dry it by pressing between the folds of a filter paper. Place it on a watch glass and try to cut it with a dry knife. We will find that the piece of sodium metal can be easily cut into small pieces.