Draw the electron dot structure of ethane molecule (${\mathrm{C}}_2{\mathrm{H}}_6$). 

Which of the four test tubes containing the following chemicals shows the brisk effervescence when dilute acid was added to them?

(i) $\mathrm{KOH}$

(ii) ${\mathrm{NaHCO}}_3$

(iii) ${\mathrm{K}}_2{\mathrm{CO}}_3$

(iv) $\mathrm{NaCl}$