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

Five young ladies (Liz, Marge, Sam, Ella and Jenny) went on five different hiking adventures. Each walked a distance of 3, 4, 5, 6, and 7 kilometers (random order). Each were able to take an extraordinary wildlife photograph in different locations (forest, meadow, mountain, river side and bushes) of different animals (rabbit, bird, deer, fox and bear cubs). From the clues below determine where and of what each girl took a photograph of, and ...

Each of the clues below is for a word that begins with "tri". The clues do not refer to the words themselves, but rather to the word that must be added to "tri". eg. "A description of three goods to encourage sales" would be "triad".

1. Where you would find three peas
2. Passing through three intermediate places on the way to your destination
3. To fish with three hooks and bait
4. To hurl three things at once
5. A ...

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.