The five metals are in the fourth row of the periodic table on the left. Melting point values increase going across the table with K < Ca < Sc < Ti < V. The number of valence electrons for each metal atom is this: K 1; Ca 2, Sc 3, Ti 4, V 5. Increasing number of valence electrons should lead to increased attractions among valence electrons and atomic cores. Increased attraction means that a higher temperature is required for the atoms to have sufficient energy to overcome attractions of their neighbors and move more freely in the liquid state. Therefore more valence electrons should correlate with higher melting points.

More valence electrons produce stronger metallic bonding. The harder a substance is the more difficult it is to make a dent in the surface. Making a dent means moving one part of the substance away from another and that should be harder the stronger the attractions are among the atoms. Therefore hardness should increase from left to right across the periodic table: K softer than Ca softer than Sc softer than Ti softer than V. (You can look up hardness values in Wikipedia to check this prediction.)

If the valence electrons are not associated with any specific atomic nucleus and core electrons, the valence electrons should be able to move easily from one atom to another. If an electric potential difference (voltage) is applied to the metal by attaching the positive and negative terminals of a battery to the metal in two places, electrons can move away from the negative terminal and toward the positive terminal, producing electric current.