A red solid is insoluble in water. However it becomes soluble if some KI is added to water. Heating the red solid in a test tube results in liberation of some violet coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid is

  • Option 1)

    (NH_{4})_{2}Cr_{2}O_{7}\;

  • Option 2)

    \; HgI_{2}\;

  • Option 3)

    \; HgO\;

  • Option 4)

    \; Pb_{3}O_{4}

 

Answers (1)

As we learnt in 

Reaction of NaOH with salts -

Forming unstable hydroxides

- wherein

HgCl_{2}+2NaOH\rightarrow 2NaCl+Hg (OH)_{2}) (unstable) \\Hg(OH)_{2}\rightarrow HgO (yellow)\downarrow+H_{2} O

 

HgI_{2}+2KI\rightarrow K_{2}\left [ HgI_{4} \right ] 
Red

K_{2}\left ( HgI_{4} \right )\overset{heat}{\rightarrow}2KI+Hg+I_{2}
                                                            Violet

 


Option 1)

(NH_{4})_{2}Cr_{2}O_{7}\;

This option is incorrect.

Option 2)

\; HgI_{2}\;

The option is correct.

Option 3)

\; HgO\;

This option is incorrect.

Option 4)

\; Pb_{3}O_{4}

This option is incorrect.

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