Which of the following languages are undecidable? Note that \(⟨M⟩\) indicates…

Which of the following languages are undecidable? Note that $⟨M⟩$ indicates encoding of the Turing machine $M$.

$L_1 = \{\left \langle M \right \rangle \mid L(M) = \varnothing \}$

$L_2= \{\left \langle M,w,q \right \rangle \mid M \text{ on input } w \text{ reaches state } q \text{ in exactly } 100 \text{ steps}\}$

$L_3= \{\left \langle M \right \rangle \mid L (M) \text{ is not recursive}\}$

$L_4= \{\left \langle M \right \rangle \mid L(M) \text{contains at least $21$ members}\}$