Question

Which of the following forms a basic oxide?
A.$B$
B.$Tl$
C.$Al$
D.$Ga$
E.None of the above

Answer 1

An oxide is a compound which is formed by combination of a metal or non metal with oxygen element. The oxide compounds are formed by fulfilling the octet rule. A basic oxide refers to an oxide which shows the characteristic of a base.

Complete step by step answer:
Normally an oxide shows the properties of acids, bases, amphoteric and neutral. The conditions for an oxide to show such properties are listed below.
Oxide which upon reaction with water give an acid is an acidic oxide
Oxide which upon reaction with water give a base is a basic oxide
Amphoteric oxides are substances which react with both acid and bases
Neutral oxides are compounds which are neither acids nor base.
Now let us consider the reactivity and properties of the oxides of group $13$ elements.
Boron ($B$): Boron is a non metal. Boron exhibits $+ 3$ oxidation state and the oxides of boron are written as ${B_2}{O_3}$. This oxide reacts with water and produces a compound known as boric acid (${H_3}B{O_3}$). Boric acid is acidic in nature as it releases hydrogen ions on treatment with water. Thus the oxides of boron are acidic in nature.
Thallium ($Tl$): Down the group non metallic character decreases. Thallium exhibits $+ 1$ oxidation state due to inert pair effect. The oxide of Thallium is written as $T{l_2}O$. When this oxide reacts with water it generates $TlOH$ which is basic in nature.
Aluminium ($Al$): Aluminium shows the properties of both metals and nonmetals and is referred to as metalloid. The non metallic character of aluminum is less than boron. The oxides of aluminum are written as $A{l_2}{O_3}$. The oxide of aluminium reacts with both acids and bases to form salts and so are amphoteric in nature.
Gallium ($Ga$): Gallium exhibits $+ 3$ oxidation state and the oxides of gallium are written as $G{a_2}{O_3}$. Like aluminium it also reacts with acids and bases to form salts and hence is amphoteric in nature.
Therefore the option B is correct i.e. $Tl$ forms a basic oxide.

Note: The properties of oxides down the group follow the trend of acidic-amphoteric-basic. The acidity or basicity of an oxide cannot be explained with increasing atomic size of the elements down the group. Only the reactivity with water, acids and bases can explain the acidic and basic nature of oxides.