Will this MagSafe power adapter work on my MacBook Air?
No.

Wattage is not an issue. Lower-powered macbooks are be paired with higher-powered power source. A 85W power adapter is basically universal to all macbooks.

2011 MBA still has MagSafe 1/original port. Visually, plug on MagSafe adapter is L-shaped, while plug on MagSafe 2 is T-shaped. Apple sell a tiny addon that makes MagSafe adapters work with newer MagSafe 2 macbooks, but the other way around doesn't work.