The correct answer is c) Thiruvananthapuram.
Gemstones like amethyst and aquamarine are occasionally found in Thiruvananthapuram, the capital of Kerala. These gemstones are found in the form of crystals in the igneous rocks of the region. Amethyst is a purple variety of quartz, while aquamarine is a blue-green variety of beryl. Both of these gemstones are prized for their beauty and rarity.
Thodupuzha, a town in the Idukki district of Kerala, is known for its amethyst mines. The amethyst found in Thodupuzha is of high quality and is exported to many countries around the world.
The aquamarine found in Thiruvananthapuram is also of high quality and is used in jewelry and other decorative items.
The other options are incorrect. Thrissur is a city in the Thrissur district of Kerala. Palakkad is a city in the Palakkad district of Kerala. Ernakulam is a city in the Ernakulam district of Kerala. Gemstones are not found in these cities.