Ou should have observed that Al, Fe, Pb, Sn, and Zn reacted with HCl. List these five metals in order of decreasing reactivity (most reactive metal first)

Al, Zn, Fe, Sn, Pb.

Explanation:

The arrangement can be done using the infomation on electrochemical series of metals.

The electrochemical series is built up by arranging various metals in order of their standard electrode potentials (or reactivity). The most negative E° values are placed at the top of the electrochemical series, and the most positive at the bottom. some of the metals are arranged as follws;  K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, H, Cu, Hg, Ag, Au (decreasing reactivity)

One can use the following to remember the arrangement: king Nathan Can Manage All Zone Freely Since Probably He Can Handle All Ages.

the number of protons in the nucleus of a given element. has slight luster and conducts electricity at high temperatures like metal.but like a nonmetal,boron is brittle and does not conduct electricity well at low temperatures. in graphite, carbon is a soft,brittle solid.it is reflective,ductile,or malleable.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.