Question

A student adds a few drops of the universal indicator to a solution of dilute hydrochloric acid. He would observe that the colour of the solution changes from colorless to:
A. red
B. yellow
C.violet
D. green

Answer 1

Hint: In chemistry, indicators are chemical compounds which indicate the presence or absence of another compound by a sign of visual change like change of colour of the solution. Such as for acidic and basic solutions. There are some examples of indicators are, methyl blue, phenolphthalein etc.

Complete step by step answer:
A universal indicator is basically a pH indicator of a solution of several compounds. This solution of universal indicator exhibits several colour changes from the range of 1-14 in the pH scale. This pH indicator indicates the acidity or basicity of the solution. For example, the colour of the cabbage juice is red because it is an acidic solution.
According to the pH scale if any solution is with lower pH value( less than 7) is acidic in nature, and if the pH of the solution is higher(greater than 7) than the solution is basic. For pure water the pH of the solution is 7.
There are some example of indicators with the pH range as follows,

Phenolphthalein	8.2-10
Bromothymol Blue	6.0-8.4
Methyl red	4.2-6.2
Phenol red	6.8-8.4

 Now, when the colour of the solution changes to red then the dilution is acidic. And when the colour is blue it is called a basic solution.
Therefore, when a student adds a few drops of the universal indicator to a solution of dilute hydrochloric acid. The colour of the solution changes from colorless to Red.

So, the correct option is A.

Note:
In chemistry pH is a scale to measure the acidity or basicity of a solution. It is can be calculated by the formula \[{\text{pH = - log}}{\left[ {\text{H}} \right]^{\text{ + }}}\], where \[{\left[ {\text{H}} \right]^{\text{ + }}}\]. is the molar concentration of hydrogen ion present in the solution. Molar concentration is also called molarity means the number of moles of a particular solute in a solvent per liter volume of solution.