(I) The positions of four elements A, B, C and D in the modern periodic table are shown below. Which element is most likely to form an acidic oxide?

As it is evident from the periodic table that elements A and B are metals, metals form basic oxides. D is the noble gas, so it will not form any kind of oxide. Element C is a non-metal, non-metal oxides react with water to form acidic solutions which liberates Hydrogen ions in the solution. Therefore, non-metals form acidic oxides which is element C.

Sol: Option (c) is correct

Explanation: The Electronic Configuration of P is 2, 8, 1, EC of Q is 2,8, 5, EC of R is 2,8, 7 and EC of S is 2,8,8.

Now, P is a metal as it has a tendency to loss one electron to complete its octet, though it is reactive but it is a metal. On the other hand, S is a noble element as it has complete octet. Therefore, P and S are incorrect. While Q and R are non-metals as they can readily accept 3 and 1 electrons respectively due to their incomplete octets. Thus, Q and R are reactive non-metals.