Let us match the compounds with their molecular formulas: (a) Borax: It is sodium tetraborate decahydrate, $Na_2B_4O_7 \cdot 10H_2O$. (b) Kernite: It is sodium tetraborate tetrahydrate, $Na_2B_4O_7 \cdot 4H_2O$. (c) Orthoboric acid: It is a weak monobasic Lewis acid with the formula $H_3BO_3$. (d) Borax bead: On strong heating, borax loses its water of crystallization and forms a transparent glassy bead consisting of sodium metaborate ($NaBO_2$) and boric anhydride/oxide ($B_2O_3$). Therefore, the correct matching is (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i).