Comprehensive and Detailed Step-by-Step Explanation:

Modifying duplex settings to double-sided:

Printing on both sides of the paper (duplex printing) reduces paper usage, making it one of the most effective environmentally friendly printing initiatives.

It directly minimizes waste and supports sustainability goals in the workplace.

Incorrect Options:

A. Requiring user authentication for printing: While this can reduce unnecessary or unauthorized printing, it does not directly address environmental objectives like saving resources.

B. Locking down printing to only certain individuals: Limiting access may reduce printing overall, but it does not actively contribute to environmentally friendly practices like duplex printing.

D. Changing the print quality settings to best: Using the "best" print quality increases toner or ink usage, which is counterproductive to environmentally friendly objectives.

Key Takeaway:

Modifying duplex settings to enable double-sided printing is the best initiative to achieve environmentally friendly goals by reducing paper consumption.