Question

A few drops of ethanoic acid were added to solid sodium carbonate. The possible results of thereactions are: [ ]a) A hissing sound was evolved
b) Brown fumes evolved.c) Brisk effervescence occurred.
d) A pungent smelling gas evolved.

Answer 1

Yes. The acid used or sodium carbonate used should be enough to produce the sound which is due to the evolution of carbondioxide. 
2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2
Option A is correct

Answer 2

Options  A is correct due to evolution of CO2