The position of how many letters will remain unchanged if each of the letter in the word ‘CERTAIN’ is arranged in English alphabetical order?

Correct — B. Write the word above its sorted form and compare column by column.

CERTAIN: C E R T A I N
Sorted: A C E I N R T

Slot 1 C against A, slot 2 E against C, slot 3 R against E, slot 4 T against I.
Slot 5 A against N, slot 6 I against R, slot 7 N against T.

No slot holds the same letter twice, so the count is zero, option (b).

Why the others are wrong

• (a)
  One — One would need some letter to land back on its own slot. Every one of the seven moves: C goes from 1 to 2, A from 5 to 1 and N from 7 to 5.
• (c)
  Four — Four is far too many. The word opens C, E, R while the sorted form opens A, C, E, so not even the first slot survives.
• (d)
  Two — Two would need a pair of fixed points. Comparing the two rows slot by slot gives seven mismatches and no match at all.

These items ask for fixed points — letters sitting in the same slot before and after sorting. The mechanical method is the only safe one.

Write the word, write its letters in alphabetical order underneath, and compare the two rows column by column. CERTAIN sorts to ACEINRT.

The word starts with C where the sorted row starts with A, and ends with N where the sorted row ends with T, so the rows are out of step at both ends. Counting fixed points by eye, without writing the sorted row, is where the mark is lost.

Key facts

• CERTAIN in alphabetical order is ACEINRT.
• No letter of CERTAIN keeps its position when the word is sorted.
• The moves are C from 1 to 2, E from 2 to 3, R from 3 to 6, T from 4 to 7, A from 5 to 1, I from 6 to 4 and N from 7 to 5.

Common traps

• Sorting in your head and assuming a middle letter must have stayed put.
• Answering One because the word and its sorted form both carry a C near the front.
• Reading the question as how many letters change, which is seven.

No directly related past PYQ was found.