Question

An element R belongs to the 3A group. Which is true with respect to R?
A.It is a gas at room temperature
B.It has oxidation state of $+ 4$
C.It forms an oxide of type ${R_2}{O_3}$
D.It forms a halide of type $R{X_2}$

Answer 1

The elements of group 3A also known as boron family starting from boron have three valence electrons in their highest-energy orbitals $(n{s^2}{p^1})$ and they are fairly electropositive and are ionized to form a $+ 3$ charges.

Complete step by step answer:
The 3A group or boron family includes boron $(B)$ , aluminum $(Al)$ , gallium $(Ga)$ , indium $(In)$ , and thallium $(Tl)$ . As mentioned in the hint, all of them are electropositive (boron being most electronegative) in nature, which means that they tend to donate electrons rather than accepting it when they react with electronegative atoms like halogens and oxygen.
Generally 3A group elements are present in solid state at room temperature. Therefore, option A is incorrect.
When it comes to oxidation states $+ 3$ and $+ 1$ are two oxidation states which are exhibited by elements of group 3A and therefore, option B is incorrect as well.
On reacting with halogens, the Boron family gives rise to trihalides of formula $R{X_3}$ . Therefore, option D is also incorrect.
With 3 electrons in the valence shell all the 3A elements reacts with oxygen to form trioxides:-
$4M + {O_2} \to 2{M_2}{O_3}$

Therefore, from the above explanation we can say that the correct option is the option C ,that is , It forms an oxide of type ${R_2}{O_3}$ .

Note:
The reactivity of group 3A elements towards oxygen increases when we go down the group Thallium $(Tl)$ has the ability to form two types of oxides, trioxide as well as monoxide, in other words It can form $T{l_2}O$ as well as $T{l_2}{O_3}$ . Also Boron is Unreactive towards oxygen in its crystalline form. However, a finely divided amorphous boron reacts with oxygen on heating to form ${B_2}{O_3}$.