Which of the following debuggers would only support an x86 architecture?

Coveant (likely Covenant) is a C2 framework used for red team operations, not a debugger.

IDA Pro (Interactive Disassembler) is a powerful disassembler and debugger that supports a wide range of architectures, including x86, x64, ARM, and more.

Immunity Debugger is based on OllyDbg and is also primarily for x86 applications, but OllyDbg is the definitive and most common example of an x86-only debugger.

OllyDbg is a well-known debugger specifically designed for and limited to the x86 (32-bit) architecture on Microsoft Windows platforms, and it does not natively support 64-bit applications or other processor architectures.