The correct option is B S Q R P
Consider the sequence of events that create a coherent sentence.
S comes first among all other parts, as "climbed the wall" joins with the pronoun "who" to identify which boy is spoken about.
Q follows S as this incident occurs next, justifying the consequences 'broke his leg'
R follows Q as 'and' is a conjunction and it connects two words or phrases.
P follows R that follows Q because the phrases "fell down" and "broke his leg" are both consequences, that are connected to the word 'and'. Also, logically, the boy would fall down first, that results in 'breaking his leg'.
Hence the logical sequence is SQRP.
Hence option B is correct.
Options A, C and D are incorrect because they do not contain the logical sequence.