The type of oxide formed by the element among Li, Na, Be, Mg, B and Al that has the least atomic radius is :

<p>The elements given are</p> <p>Li, Na, Be, Mg, B and Al</p> <p>2$^{nd}$ period elements $\to$ Li, Be, B</p> <p>Order of atomic radii $\to$ Li > Be > B</p> <p>3$^{rd}$ period elements $\to$ Na, Mg, Al</p> <p>Order of atomic radii $\to$ Na > Mg > Al</p> <p>In a period, atomic radii decreases on moving from left to right.</p> <p>So, the element with least atomic radii in 2$_{nd}$ period (Li, Be, B) is B. The element with least atomic radii 3$_{rd}$ period (Na, Mg, Al) is Al.</p> <p>In B and Al $\Rightarrow$ B and Al are same group elements. Down the group, radii increases. So, B has least radii.</p> <p>B is the element with least atomic radius to form the oxide $A_2O_3$.</p> <p>Oxidation states of the A in oxides :</p> <p>$${A_0} \to + 2\,\,{A_{{0_2}}} \to + 2\,\,{A_{{2^0}}} \to + 1\,\,{A_{2_3^0}} \to + 3$$</p> <p>B outer configuration is s$^2$P$^1$. 3 valence electrons and form A$_2$O$_3$ type oxide.</p>