"It also uses technology to ensure safety and security of the city, something which critics argue, will lead to a surveillance state."
critics argue because of perception that smart city promotes surveillance that makes statement ( iv) correct.
There is nothing mention in passage about encouragement about formation of surveillance states so that makes statement (i) false.
And, "will lead to a surveillance state tis makes " this line makes statement (ii) false.
and there is nothing mention about " both Sustainability and surveillance" in passage so statement (iii) is wrong too.
Hence only statement (iv) is correct which is option C .