Plants depend on the atmosphere for the largest source of: phosphorus carbon weed control nitrogen

Plants depend on the atmosphere for its largest source of CARBON which it takes in in the form of Carbon Dioxide.

This answer can be achieved by the process of elimination:

Most of the earth's Phosphorus resides in the earth in its mineral form and plant gets its phosphorus from the mineral being dissolved in water.

Weed control has little to do with the atmosphere.  The control of weed is either done by human impact or in the case of some plants, it has the ability to control weed on its own through secretions.

Majority of plants cannot take in Atmospheric Nitrogen (the only exception are leguminous plants which have rhizobia in root nodules that convert atmospheric nitrogen into soluble nitrates and nitrites that can be used by the plant).  For the rest of the plant species, nitrogen's uptake in the plant rest mainly in the hands of nitrogen dissolved in groundwater.  

The correct answer would be b. carbon dioxide (6 co2) + water (6 h2o) > glucose (c6h12o6/ sugar) + oxygen gas (6 o2)

Iwould say silver and gold