The position(s) of how many letters will remain unchanged if all the letters in the word ‘ASTEROID’ are arranged in English alphabetical order?

Correct — C. Write the word over its sorted form and compare column by column.

ASTEROID → A S T E R O I D
sorted → A D E I O R S T

Rule: count only the columns where the two rows show the same letter.

Column 1 is A above A, so that position holds.
Columns 2 to 8 read S/D, T/E, E/I, R/O, O/R, I/S, D/T — every one differs.

Exactly one position survives, option (c).

Why the others are wrong

• (a)
  None — None ignores column 1. A is both the first letter of ASTEROID and the first letter alphabetically, so it cannot move.
• (b)
  Two — Two needs a second letter already standing in its sorted slot. Checking columns 2 to 8 one by one, not one of them does.
• (d)
  Three — Three is impossible here: after A the sorted row runs D, E, I, O, R, S, T while the word runs S, T, E, R, O, I, D, and the rows never agree again.

The method is mechanical and takes about twenty seconds. Write the letters of the word in a row, write the same letters sorted alphabetically directly underneath, then tick every column where the two match.

Do not reason about which letters ought to move — sort first, compare second.

The two ends are the quickest wins. The alphabetically first letter holds only if it already starts the word, and the alphabetically last letter holds only if it already ends it.

Key facts

• ASTEROID sorted alphabetically is A D E I O R S T.
• Only the first position, the letter A, is the same in both rows.
• The word has eight letters and no repeats, so no column is ambiguous.

Common traps

• Sorting the letters and then forgetting to compare against the original positions
• Counting a letter as unchanged because it is still present rather than in the same slot
• Rushing past column 1, which is where the only match sits

No directly related past PYQ was found.