Q26

Which of the following languages are undecidable? Note that $\left \langle M \right \rangle$ 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}\}