IMAT 2011 Q67 [Transition Elements]

One group of elements in the Periodic Table contains, in descending order, boron, aluminium, gallium, indium and thallium. Which of the following are correct about these elements?

  1. Indium forms the oxide {In_2O_3}
  2. Boron is the least reactive element in the group
  3. Gallium forms the sulphate {GaSO_4}

A. 1 only
B. 1 and 2
C. 1 and 3
D. 2 and 3
E. 1, 2 and 3

The group in question is group 13. The elements of this group have 3 valence electrons and thus, usually have an oxidation number of +3.
So the first is correct and the third is false since SO4 has an oxidation state of -2 (You should know it as it is one of the polyatomic ions you should memorize for the exam).
Last but not least, we should know that the reactivity trend increases from top to bottom, meaning that boron is the least reactive element of the group so the 2nd statement is also correct and the answer to the question is B.