# Among the species A: $CrC{{l}_{3}}$; B: $CuS$; C: $AlC{{l}_{3}}$; D: $ZnC{{l}_{2}}$; which will be soluble in excess of NaOH?(a)A,C and D(b)C and D only(c)B and C only(d)A and D only

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Hint: Some of the inorganic compounds do not react with NaOH. Some when reacted with NaOH can produce inflammable gas. More polar metal salts can dissolve in excess of NaOH. d-block metal salts are more polar salts.

Chromium chloride when react with NaOH it gives chromium hydroxide and the salt NaCl.
When $CrC{{l}_{3}}$ reacts with excess NaOH to give a complex and the salt NaCl.
$CrC{{l}_{3}}+6NaOH\to Na[Cr{{(OH)}_{6}}]+3NaCl$
Aluminium chloride reacts with NaOH to give aluminium hydroxide and salt.
When excess NaOH reacts with $AlC{{l}_{3}}$ will give $NaAl{{O}_{2}}$ and water. The reaction is given as
$AlC{{l}_{3}}+3NaOH\to NaAl{{O}_{2}}+2{{H}_{2}}O$
When $ZnC{{l}_{2}}$ reacts with excess NaOH, it gives zinc hydroxide and a salt NaCl.
$ZnC{{l}_{2}}+2NaOH\to Zn{{(OH)}_{2}}+2NaCl$
Only CuS does not react with NaOH to give any hydroxide or complex. This is because copper itself is highly unreactive. It does not dissolve in NaOH until it is highly concentrated. Also CuS is less polar than the other options above.
Thus, only $CrC{{l}_{3}}$ , $AlC{{l}_{3}}$ and $ZnC{{l}_{2}}$ react with excess of NaOH.

The correct answer for the question is option (a).