NIMCET 2025 Paper

Consider a system with a CPU having 6 registers and 32-bit instructions.
The maximum possible size of the main memory is $512\mathit{K}\mathit{B}\left(1\mathit{K}=2^{10}\right)$.
Each instruction takes two registers and one memory address as operands.
Which one of the following correctly gives the maximum possible number of distinct instructions that can be present in the instruction set of the CPU?