Which loan is less common and typically has fluctuating payments throughout the loan period?

The adjustable-rate mortgage is the correct choice because it is characterized by interest rates that can fluctuate at specific intervals throughout the loan term. Unlike fixed-rate mortgages, which have a static interest rate and consistent monthly payments, adjustable-rate mortgages start with a lower interest rate that is often fixed for an initial period before adjusting at predetermined intervals based on market conditions. This means that the monthly payments can vary significantly after the initial fixed period as the interest rate changes, making them less predictable for borrowers.

Comparatively, fixed-rate mortgages offer stability with fixed payments throughout the loan's duration. Conventional and hybrid mortgages may have fixed or adjustable components, but they typically do not exhibit the same degree of fluctuation in payments as seen in adjustable-rate mortgages, especially after the fixed-rate phase in hybrids. Thus, while options like fixed-rate and conventional mortgages are more common and predictable in their payment structure, adjustable-rate mortgages are known for their variability, leading to fluctuation in payments.