Step 1:
Process costing is used where production is continuous and goods pass through several stages of production.
Step 2:
Industries such as steel, paper, chemicals, soaps, and medicines use process costing because production takes place in sequential processes.
Step 3:
Both Assertion and Reason are correct.
The reason correctly explains why process costing is suitable for such industries.
Step 4:
Hence, the correct answer is:
\[
\boxed{\text{(1)}}
\]