With reference to 'Silver articles', which of the following statements is/are correct ?
1. Silver articles turn black after some time when exposed to air.
2. It happens due to coating of silver sulphi

Question

With reference to 'Silver articles', which of the following statements is/are correct ?
1. Silver articles turn black after some time when exposed to air.
2. It happens due to coating of silver sulphide.
Select the correct answer from the code given below :
Code :

UnlockIAS · Accepted Answer

Correct — B, Both 1 and 2. Statement 1 is the everyday observation: a silver ornament, coin or spoon left in the open loses its shine and goes dull grey and then black. Statement 2 gives the right reason for it. The black film is silver sulphide, Ag2S, described in the chemical literature as a dense black solid. It forms because silver reacts with the traces of hydrogen sulphide present in ordinary air — hydrogen sulphide, not oxygen, is what silver needs in order to tarnish, and plain oxygen blackens it only very slowly over long periods. The layer is also self-limiting: once a coating of silver sulphide has formed it shields the metal underneath from further attack, which is why tarnish stays a surface film and does not eat through the article. Both statements therefore stand, and both are about the same event.

Why the other options are wrong — (a) It accepts the chemistry but rejects the observation that produced it, which is self-contradictory. If a coating of silver sulphide forms on the article, the article must change colour — silver sulphide is black, so statement 1 follows from statement 2.  (c) Both statements are correct. Silver does tarnish on exposure to air, and the tarnish is a silver sulphide film. Ruling out both would mean silver never darkens, which contradicts ordinary experience with silverware and silver jewellery.  (d) The observation is right but the explanation is wrongly rejected. This is the option for a candidate who assumes tarnishing must be oxidation and expects silver oxide. The blackening of silver is specifically a sulphide reaction — it is copper that goes green with a basic carbonate and iron that goes reddish-brown with a hydrated oxide.

Concept: Corrosion is the slow chemical attack of a metal by substances in its surroundings, and it produces a different-coloured compound on the surface in each case. Iron rusts to a flaky reddish-brown hydrated oxide, copper acquires a green coat of basic copper carbonate, aluminium forms a thin colourless film of aluminium oxide that protects the metal beneath, and silver blackens with silver sulphide. Silver is the odd one out because the culprit is not oxygen but sulphur: the small quantities of hydrogen sulphide that occur in air are enough to convert the bright surface into Ag2S, a compound that also occurs in nature as the minerals acanthite and argentite.

State PCS 2025 Q75 — Science & Technology PYQ with Answer

State PCS 2025 Q75 — Science & Technology PYQ with Answer