Step 1: Analyzing MAK Halliday.
MAK Halliday is associated with the theory of Functionalism in linguistics. Therefore, P is associated with iii.
Step 2: Analyzing Leonard Bloomfield.
Leonard Bloomfield is a key figure in American Structuralism, thus Q is associated with iv.
Step 3: Analyzing BF Skinner.
BF Skinner is a major figure in Behaviourism, particularly in the field of psychology, which makes R associated with i.
Step 4: Analyzing Jean Piaget.
Jean Piaget is a central figure in the development of Cognitivism, making S associated with ii.
Thus, the correct matching is:
P – iii, Q – iv, R – i, S – ii.