Which of the following is/are undecidable?

Consider the following languages:

L₁ = {aⁿ waⁿ | w $$\in$$ {a, b}*}

L₂ = {wxw^R | w, x $$\in$$ {a, b}*, | w | , | x | > 0}

Note that w^R is the reversal of the string w. Which of the following is/are TRUE?

Consider the following languages:

$$\eqalign{ & {L_1} = \{ ww|w \in \{ a,b\} *\} \cr & {L_2} = \{ {a^n}{b^n}{c^m}|m,\,n \ge 0\} \cr & {L_3} = \{ {a^m}{b^n}{c^n}|m,\,n \ge 0\} \cr} $$

Which of the following statements is/are FALSE?

The ___________ is too high for it to be considered __________.