1. IDEA. This one was tough. Take the last letter of the last word (A in IDEA), the second to last letter of the second to last word (B in BABE), & so on, & you will find that the letters are in alphabetic order.
2. The three letter word is SUN, & the word that does not belong is RANGE.
3. If you add the letter B to each "word" in the sequence, you get bad, big, bog, bra, cab, lab, & the only option given that makes a word with a B added to it, or, to make orb. When a B is added to each word, the words are in alphabetic order.
4. arist. Add OCRACY to the end of this "word" & the others in the set, & you have words that denote forms of government.
5. 213. The difference between 7 & 8 in the first number, 78, is 1. The difference between the 6 & 9 in 69 is 3; then you have 5 for 5 & 0 in 50, 7 for 4 & 11 in 411, 9 for 3 & 12 in 312, & 11 for 2 & 13 in 213. Yet another tough puzzle!
6. It is extremely unusual that none of the words contain the letter E, which is found in a large portion of the words in the English language.