Select the correctly spelt word to fill in the blank. Calder Hall is a nuclear power station in England which is known as the first nuclear power station to generate electricity for ___________ purposes.

Correct — D. The word is commerce plus the suffix -ial.

Commerce carries a double m, and the suffix does not disturb the stem, so both m's survive.

The silent final e of commerce is dropped before a suffix beginning with a vowel: commerce becomes commercial.

That gives two m's, one r and the ending -cial — option (d).

Why the others are wrong

• (a)
  comercial — Has a single m. Commerce is spelt with mm and the suffix leaves the stem alone, so the double m has to survive.
• (b)
  comercail — Single m again, and the ending is transposed to -cail. The English adjective ending is -ial, giving -cial.
• (c)
  commerceil — Keeps the double m but holds on to the e of commerce and ends -ceil. The e is dropped before the vowel suffix, so the ending is -cial.

Spelling items in this format offer one correct form and three near misses, so they are won by knowing where the word comes from rather than by how it looks on the page.

Commercial is built on commerce. Two features carry straight over: the double m, and the c before the ending.

What changes is the final e, dropped whenever a suffix beginning with a vowel is added. The same rule turns finance into financial and office into official.

Key facts

• Commercial is commerce plus -ial, keeping the double m.
• A final silent e is dropped before a suffix that begins with a vowel.
• The same stem gives commerce, commercially and commercialise.

Common traps

• Writing comercial with a single m, which two of the four options do.
• Choosing by sight rather than by stem, when every distractor is built to look plausible at a glance.

No directly related past PYQ was found.