A)4
B) 6
C) 1
D) 7
E) 3
You can tell by how far along they are in the table. It is easy to see in the first few rows, but harder to tell later on. However, the elements beneath the top elements follow the same trend.
Fluorine, for instance, is the 7th element of 8 in the second row. Therefore, it has 7 valence electrons. Iodine, I, which is in the same period also has 7 valence electrons.
Carbon has 4 because it's the 4th one in the row.
K, potassium, has 1 because it's in the first period.
B, Boron, has 3 because it's in the "3rd period." (not including the transition metals)
S, Sulfur, has 6 because it's in the "6th period" (yet again skipping the transition metals will help you tell how many valence electrons it has).
Barbara McClintock, who discovered transposable elements.
Periodic Table of the Elements
The Bohr model of the atom. The nucleus contains protons and neutrons, and electrons orbit around ...
The Elements of Cognition
Periodic table of the elements
Mutations in cis-regulatory elements of Ultrabithorax cause homeotic transformations