The correct answer is B. Cadmium.
Potassium, sodium, and lithium are all alkali metals that react violently with water to produce hydrogen gas. Cadmium, on the other hand, is a transition metal that does not react with water.
Alkali metals are very reactive because they have a single valence electron in their outer shell. This electron is easily lost, which makes alkali metals highly electropositive. When an alkali metal is placed in water, the water molecules surround the metal and form a hydration shell. The hydrogen atoms in the water molecules are attracted to the electronegativity of the metal, and they are pulled away from the oxygen atoms. This results in the formation of hydrogen gas and hydroxide ions.
The reaction of alkali metals with water is very exothermic, meaning that it releases a lot of heat. This heat can cause the water to boil and the metal to melt. In some cases, the reaction can be so violent that it can cause the metal to explode.
Cadmium, on the other hand, is a transition metal. Transition metals have a filled d subshell in their outer shell. This means that they are not as reactive as alkali metals. When cadmium is placed in water, the water molecules do not surround the metal in the same way that they do for alkali metals. The hydrogen atoms in the water molecules are not as strongly attracted to the metal, and they are not pulled away from the oxygen atoms. This results in a much weaker reaction than the reaction of alkali metals with water.
In fact, cadmium is so unreactive that it can be used to line pipes that carry water. This is because the cadmium
will not react with the water and corrode the pipe.