Which one of the following is the lowermost/innermost intrusive igneous rock ?

Intrusive igneous rocks, or plutonic rocks, are formed when magma cools and solidifies deep within the Earth's crust. The classification of these landforms is based on their shape and depth:

• Batholiths: These are the largest and deepest intrusive bodies. They are massive granitic structures that cool at great depths, often forming the core of mountain ranges. Due to their formation at the deepest levels of the crust, they are the lowermost/innermost structures.
• Laccoliths: Large dome-shaped intrusive bodies with a level base, connected by a pipe-like conduit from below, typically found at shallower depths.
• Lopoliths: Igneous intrusions that are saucer-shaped (concave to the sky).
• Phacoliths: Lens-shaped masses of igneous rocks that occupy the crest of an anticline or the base of a syncline.

Since batholiths represent the foundation of plutonic activity at the greatest depths, Option B is correct.