An inorganic compound 'A' shows the following reactions
i) It is white solid, exists as dimer and fumes in wet air
ii) It sublimes at 180°C and forms monomer if heated to 400°C
iii)Its aqueous solution turns blue litmus to red and gives a white precipitate with AgNO₃ solution which is soluble in NH₄OH
iv) Addition of NH₄OH and NaOH separately to the solution of 'A' gives a gelatinous precipitate which in however soluble in excess of NaOH. 
The compound 'A' is

Compound B is Al₂​Cl₆​.

(i) Al₂​Cl₆​ is a white solid, exists as dimer and fumes in wet air.

(ii) It sublimes at 180°C and converts into AlCl₃​ at 400°C.

(iii) Its aqueous solution is acidic, so it turns blue litmus to red.

${\mathrm{Al}}_2{\mathrm{Cl}}_6+6{\mathrm{H}}_2\mathrm{O}\to \underset{\mathrm{weak} \mathrm{base}}{2\mathrm{Al}{\left(\mathrm{OH}\right)}_3}+\underset{\mathrm{strong} \mathrm{acid}}{6\mathrm{HCl}}$

It gives white ppt. with AgNO₃​ which is soluble in NH₄​OH.

(iv) ${\mathrm{AlCl}}_3+3\mathrm{NaOH}\to \underset{\left(\mathrm{white} \mathrm{ppt}.\right)}{2\mathrm{Al}{\left(\mathrm{OH}\right)}_3}+3\mathrm{NaCl}$

      $\mathrm{Al}{\left(\mathrm{OH}\right)}_3+\underset{\mathrm{excess}}{\mathrm{NaOH}}\to \underset{\mathrm{soluble}}{{\mathrm{NaAlO}}_2}+2{\mathrm{H}}_2\mathrm{O}$

But in case of NH₄​OH, the ppt. of Al(OH)₃​ does not dissolve in excess of NH₄​OH.