Final answer:
The destination register for the add operation 'add r1, r2, r3' is r1, where the sum of the values in r2 and r3 will be stored.
Step-by-step explanation:
The instruction add r1, r2, r3 is from assembly language, which is used in computer programming to manage hardware operations. This instruction specifies an addition operation where r2 and r3 are the source registers whose values are to be added together, and r1 is the destination register where the result of the addition will be stored. In other words, the value in r2 is added to the value in r3, and the sum is placed in r1. This is a common operation in lower-level programming languages that interact directly with the processor's architecture.