Answer: Option C. -> Aqueous solution of either weak acids or weak bases.
:
C
pH indicators are aqueous solutions of either weak acids or weak bases. They are chemical detectors of hydrogen ions ($H^{+1}$) and hydroxideions ($O{H}^{-1}$) . It is added in small quantity to a solution to determine the pH.

Answer: Option B. -> Decreases 
:
B
When HCl gas is passed through a saturatedNaClsolution, the number of ${\text{Cl}}^{-1}$ ions increases. The increased number of${\text{Cl}}^{-1}$ interact with ${\text{Na}}^{+1}$ ions to form crystallised NaCl. Thus, the solubility of NaCl decreases and it is recovered in crystalline form. This phenomenon is called "common ion effect".

Answer: Option A. -> NaOH(aq) + HCl(aq)→ NaCl(aq) + H2O(l)
:
A
When an acid reacts with a base, it forms salt and water. This is called neutralisation reaction.
Here, only the reaction between hydrochloric acid with sodium hydroxide is a neutralisation reaction since it gives sodium chlorideand water as products. The reaction involved is given below:
$\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{aq}\right)+H_{2}O\left(l\right)$

Answer: Option B. -> Water
:
B
Battery acid, vinegar and soda are all acids from the given options.All acids have pH value less than 7. Battery acid and vinegar have pH values of 0.8 and 2.4 respectively. The pH value of soda ranges from approximately 2.2 to 3.3.
Water has a pH value of 7 if there are no impurities in it.
Hence from the given options, water has the highest pH value.

Answer: Option B. -> hydrogen
:
B
Acidsreact with metals to producetherespective metalsaltalong withhydrogen gas. The general form of the reaction is given below:
$\text{Acid (aq)}+\text{Metal (s)}\to \text{Salt(aq)}+\text{Hydrogen (g)}$
For example:
When hydrochloric acid reacts with zinc, itproduceszinc chloride along with the evolution ofhydrogen gas.
The chemical reaction is given below:
$2\text{HCl (aq)}+\text{Zn (s)}\to {\text{ZnCl}}_2\text{(aq)}+{\text{H}}_2\text{(g)}$

Answer: Option B. -> H2SO4
:
B
Strength of acid depends on the ability of the compound to donate the proton and thenumber of protons it can donate inthe solution. Among all the given acids ${\text{H}}_2{\text{SO}}_4$ has maximum ability to donate $H^{+}$ in the aqueous solution. Also, ${\text{H}}_2{\text{SO}}_4$ can donate two $H^{+}$ ions per molecule while all other acids can donate only one $H^{+}$ ion in the solution. Hence,${\text{H}}_2{\text{SO}}_4$ is the strongest acid among the given acids.

Answer: Option C. -> Antacid
:
C
Indigestion causes acidity in the stomach. We add anti-acids to neutralise it. The antacids are basic in nature and hence neutralise the acids. Magnesium hydroxide (milk of magnesia) is a commonly used antacid.

Answer: Option A. -> 1M hydrochloric acid
:
A

Strong acids release ${\text{H}}^{+}$ ions more easily than weaker ones. Hydrochloric acid $(\text{HCl}$) is a strong acid, whereas, acetic acid $\left({\text{CH}}_3\text{COOH}\right)$, citric acid $\left({\text{C}}_6{\text{H}}_8{\text{O}}_7\right)$ and propanoic acid $\left({\text{CH}}_3{\text{CH}}_2\text{COOH}\right)$ are weak acids.
So, 1M hydrochloric acid will have a higher concentration of ${\text{H}}^{+}$ ions than acetic acid and propanoic acid.

Answer: Option A. -> True
:
A
For any substance to conduct electricity, there must be the availability of mobile charge carriers. These charge carriers can be:
$\bullet$ free electrons that can flow within the substance.
$\bullet$ ions that can flow in the solution.
An acid when added in water dissociates into its corresponding ions. For example, hydrochloric acid (HCl) when added to water, dissociates into ${\text{H}}^{+}$ and ${\text{Cl}}^{-}$ ions. These ions present in the solution conduct electricity.

Answer: Option B. -> Alkalis
:
B

A base is any substance that neutralises an acid. It may or may not be soluble in water. Those bases that are soluble in water are known as alkalis. Thus, an alkali is a water soluble base. For eg., NaOH, KOH etc.