Is gas given with oxygen to patients for diagnosis of breathing problem?

If the pH value of a substance is lower than 7, it would be considered as–

Which of the following is the most common kidney stone-forming compound?

What is the mass number of an element, the atom of which contains two Protons, two neutrons and two electrons? 

The air is the example of:

In which of the following chlorine has + 1 oxidation number?

Permanent hardness of water may be removed by the addition of

Washing soda is the common name for