GKFix MCQ Question

What is the expression for mutual inductance M12 for two long co-axial solenoids?

• A. µ₀n₁n₂πr₂²l
• B. µ₀n₁n₂πr₁²l
• C. µ₀n₁²πr₁²l
• D. µ₀n₂²πr₂²l