$1.$ What is the primary source of hard water?

a$)$ Rainwater

b$)$ Underground springs

c$)$ Surface water

d$)$ River water

Which of the following ions is primarily responsible for hardness in water?j

a$)$ Sodium ions

b$)$ Chloride ions

c$)$ Calcium ions

d$)$ Potassium ions

What is the acceptable limit for hardness in drinking water, as per WHO standards?

a$)100$ ppm

b$)200$ ppm

c$)500$ ppm

d$)1000$ ppm

Which method is commonly used to estimate the hardness of water?

a$)$ Gravimetric method

b$)$ Titration method

c$)$ Spectrophotometric method

d$)$ Chromatographic method