P-NP Theory

The problem 3-SAT and 2-SAT are

Language L_{1} is polynomial time reducible to language L_{2}. Language L_{3} is polynomial time reducible to L_{2}, which in turn is polynomial time reducible to language L_{4}. Which of the following is/are true?
I. if L_{4} \in P, then L_{2} \in P
II. if L_{1} \in P or L_{3} \in P, then L_{2} \in P
III. L_{1} \in P, if and only if L_{3} \in P
IV. if L_{4} \in P, then L_{1} \in P and L_{3} \in P

Consider two decision problems Q1,Q2 such that Q1 reduces in polynomial time to 3-SAT and 3-SAT reduces in polynomial time to Q2. Then which one of the following is consistent with the above statement?

Consider the decision problem 2CNFSAT defined as follows:
{ \phi | \phi is a satisfiable propositional formula in CNF with at most two literal per clause}
For example, \phi =(x_{1} \vee x_{2}) \wedge (x_{1} \vee \bar{x_{3}}) \wedge (x_{2} \vee x_{4}) is a Boolean formula and it is in 2CNFSAT.
The decision problem 2CNFSAT is

Suppose a polynomial time algorithm is discovered that correctly computes the largest clique in a given graph. In this scenario, which one of the following represents the correct Venn diagram of the complexity classes P, NP and NP Complete (NPC)?