Select the most appropriate idiom for the given group of words. A time when money might unexpectedly be needed

Correct — D. The clue words in the definition are money and unexpectedly needed, which point to saving against a future shortage.

A rainy day is that shortage. The idiom lives in save for a rainy day: put money aside for a time of unexpected need.

None of the other options is about money at all → option (d).

Why the others are wrong

• (a)
  A rash of something — A rash of something means a sudden run of unwelcome events in a short period, as in a rash of burglaries. It marks frequency, not a need for savings.
• (b)
  A raw deal — A raw deal means unfair or harsh treatment. Someone underpaid gets a raw deal, but the phrase names an injustice, not a time of need.
• (c)
  A rap over the knuckles — A rap over the knuckles means a mild reprimand for a small offence. It is a punishment idiom, with nothing about money set aside.

An idiom is fixed: the words carry a meaning the parts do not, and swapping one word usually kills it.

A rainy day stands for a period of difficulty, especially financial, and the full form is save for a rainy day.

The image is old and plain — rain stops outdoor work, work stops income, so you need a reserve. When SSC gives the definition and asks for the idiom, find the concrete noun in the definition, here money, and pick the stock phrase that is about that noun.

Key facts

• Save for a rainy day means to set money aside for a time of unexpected need.
• A raw deal means unfair treatment.
• A rap on or over the knuckles means a mild reprimand.
• A rash of something means a sudden run of similar unpleasant events.

Common traps

• Picking a raw deal because it sounds financial
• Reading the options as literal descriptions instead of fixed phrases

No directly related past PYQ was found.