What is the number of $$\mathrm{=N-OH}$$ groups present in dimethyl glyoximato?

Work done when 2 mole of an ideal gas is compressed from a volume of $$5 \mathrm{~m}^3$$ to $$2.5 \mathrm{~m}^3$$ at 300 K, under a pressure of 100 kpa is

Which of the following pairs of aryl halides cannot be prepared directly by electrophilic substitution?

Which of the following reaction of diazonium salt involves retention of diazonium group?