The correct answer for why ginger is considered as a stem and not a root is option 3: It has nodes and internodes. Nodes are the points along a stem where leaves, buds, or flowers are attached, while internodes are the segments between these nodes. In the case of ginger, it has visible nodes and internodes that can be identified when it is cut or examined closely. This characteristic is typical of stems, not roots.

Option 1, storing food material, can be true for both stems and roots. Option 2, growing horizontally in the soil, is not a defining characteristic of stems but rather a growth habit observed in some plants. Option 4, lacking chlorophyll, is not specific to either stems or roots, as some stems and roots do not have chlorophyll.

Therefore, the presence of nodes and internodes is the key characteristic that classifies ginger as a stem.