A member of the Lamiaceae family: Notice the square stem, covered in hairs, with the opposite leaves. Also, the purple hue to the leaves lead me to believe this plant is Purple Dead Nettle.
A member of the Apiaceae family: The defining character was the flowers are arranged in an umbel. Common name Wild Carrot.
A plant that produces achenes: These dry, indehiscent fruits are numerous inside sunflowers. Sunflower “seeds” are not really seeds but achenes.
A plant with prickles: You would consider these prickles because they are easily taken off the epidermis of the plant and are not modified leaves or shoots. They are softer then thorns or spikes and cover the entire stem, not a few areas on this Teasel.
Acer Rubrum: Also known as red maple, these simple leaves are lobed. The defining character would have to be the red color of the leaf.
Aster novae-angliae: Also known as New England Aster, the flower has a purple color with numerous petals with radial symmetry.