Which element in Group B can be added to Group A? Why?

Group A: Iridium, Vanadium, Xenon, Lanthanum, Carbon, Dysprosium
Group B: Radon, Barium, Uranium, Platinum, Manganese, Phosphorus

Letter Equations are well known phrases or facts where the key words have been replaced with the first letter of that word. These are often in the form of an equation, which contain a number, an = sign and the rest of the obscured phrase or fact.

3 = S in the F V of C C (N, P, S M)

Change COLD to HEAT by changing one letter at a time. Each change must produce a valid word in the English language. But there is a catch. You must make the change by going through COOL and WARM. No word can be used more than once.

COLD ---- COOL ---- WARM ---- HEAT

The following not only describes a book, but it's an anagram for the title. What is it?

Huge water tale stuns. End had you tense.