anaerobic monerans which are endosymbiotically associated with cattles rumen are

1. bacillus
2. methanobacterium
3. halococcus
4. thermoacidophiles

The correct option is 4.
A thermoacidophile (combination of thermophile and acidophile) is an extreme archeon which thrives in acidous, sulfur rich, high temperature environments.

Thermoacidophiles prefer temperatures of 70 - 80 °C and pH between 2 and 3. They live mostly in hot springs and/or within deep ocean vent communities. Classified as an archeon and an extremophile, Thermoacidophiles are found in places where most organisms would not survive.