Four metals, labelled R, T, X and Z, have the following characteristics:

• R fizzes when added to dilute hydrochloric acid.
• T is precipitated when R reacts with an aqueous solution of a compound of T.
• X is the only one of these metals that occurs naturally on Earth uncombined with other
  elements.
• Z is the only one of these metals manufactured commercially by electrolysis of one of its
  molten compounds, whereas R and T can be manufactured by heating their oxides with
  carbon.
  What is the order of reactivity of these metals, from most to least reactive?

Answer:

14) F

T is precipitated when R reacts with aqueous solution of T. This means that R replaces T. Therefore R is more reactive than T.
X is the only metal out of the four that does not combine with other elements. X is the least reactive out of the four.
Z is obtained by electrolysis whereas R and T are obtained by heating their oxides with carbon. Carbon replaces the less reactive metal in a redox reaction, where the carbon is oxidised and the metal is reduced. Therefore, the metals that are obtained from heating with carbon are less reactive than the metals obtained from electrolysis. Therefore, Z is the most reactive element.
Z, R, T, X