Which is the strongest metal ( excluding alloys ) existing in earth( which are known to us)
Tungsten ( W ) metal is the strongest metal on earth.
It might be difficult to determine the "strongest" metal when considering the different characteristics attributed to metals. That said, it is probably tungsten that is the strongest of the metals (in pure form). It has the highest tensile strength of all pure metals. Alternately, titanium could be considered the strongest, as it has the highest strength-to-weight ratio of any metallic element.
However, it is not possible to answer this question definitively, as there are three measures of strength:
Tensile strength (the ability to withstand being pulled apart without deforming),
Compressive strength (the ability to withstand being compressed without deforming), and
Shear strength (the ability to resist forces perpendicular to the items main axis, rather than along it, as with tensile or compressive forces).
All metals have different characteristics, and the strongest in each category is not the same.