Which of the following is the most reactive? * O Thallium O Gallium O Indium O Boron

Thallium

Thallium is highly reactive, readily soluble in acids, and forms monovalent thallous and trivalent thallic salts, the latter being less stable.

Gallium is a fairly reactive element, it combines with most non-metals at high temperatures, and it reacts with both acids and alkalis. An alkali is a chemical with properties opposite those of an acid.

Indium is a non-combustible solid in bulk form but is flammable in the form of a dust, it reacts with strong oxidizing agents and reacts explosively with dinitrogen tetraoxide dissolved in acetonitrile.

Boron is a poor conductor of electricity, and is fairly non-reactive, although it is water soluble.