Songs that express grief and lamentations are known as:

Mangala Isai
Oppari
Silambu Paadalgal
Themmangu

The correct answer is: b) Oppari.

Oppari is a genre of Tamil folk music that is traditionally performed by women to express grief and lamentations. The songs are often about the death of a loved one, and they can be very moving and emotional. Oppari is often performed at funerals and other mourning ceremonies, and it can help to provide comfort and support to those who are grieving.

Mangala Isai is a genre of Tamil music that is traditionally performed at weddings and other auspicious occasions. The songs are often about love, happiness, and prosperity. Mangala Isai is usually performed by a group of musicians, and it can be very lively and festive.

Silambu Paadalgal are a type of Tamil folk song that is traditionally sung by women. The songs are often about love, marriage, and family life. Silambu Paadalgal are usually accompanied by the playing of the silambattam, a traditional Tamil drum.

Themmangu is a type of Tamil folk music that is traditionally performed by men. The songs are often about war, heroism, and love. Themmangu is usually accompanied by the playing of the thavil, a traditional Tamil drum.