This code is used to add two 8-bit numbers and the sum is also a 8-bit number. here H-L pair is used to store the two numbers. Usually LXI command is used to load immediate 16-bit data in the register pair designated in the operand
This LXI command is a 3-byte instruction. First byte is used for mnemonics, second byte specifies lower order byte and 3rd byte specifies higher order byte.
Code:
Mnemonics       Operands             Comments
LXI                   H,2501 H             Get address of 1st number in H-L pair.
MOV                 A,H                     1st number in accumlator.
INX                   H                        increment content of H-L pair.
ADD                  M                        Add 1st and 2nd numbers.
STA                  2503 H                Store sum in 2503 H.
HLT
INX is used to increment the register pair by 1.