Sentence improvement — first conditional with 'if' about tomorrow: use present simple in the if-clause — 'if it rains tomorrow' — not 'shall/will'.

Given sentence
I will not go to school, if it shall rain tomorrow.

Concept/Approach
In real future conditions (first conditional), the if-clause takes present simple; the main clause takes future: 'If it rains tomorrow, I will not go to school.' 'Shall/will' are not used in the if-clause.

Correction
if it rains tomorrow

Eliminating options
'would rain' → unreal/second-conditional suggestion.'will rain' → wrong in the if-clause.'No improvement' → keeps the modal error.

Final Answer
it rains tomorrow