Test: Atomic And Molecular Mass - Class 9 MCQ

Silver has the symbol Ag, not Si.

Sodium has the symbol Na, not So.

Potassium has the symbol K, not Pt.

Sulphur has the correct symbol S, so this is the correct pair.

The valency of hydrogen is 1 and the valency of sulphur is 2. To balance the valencies, we need 2 hydrogen atoms for every 1 sulphur atom.

Therefore, the formula of hydrogen sulphide is H₂S

An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon 12. The mass of any isotope of any element is expressed in relation to the carbon 12 standard.

The wrong thing in writing cobalt as CO is that we can't write o as O because O represent Oxygen and symbols representing an element with two letters have first one as capital and next one should be in small letter.

Therefore we should always write cobalt as..Co not CO!

Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number 79. 

- The atomic number of an atom is the number of protons in its nucleus.
- An atom with an atomic number of 11 has 11 protons.
- The correct answer is A: 11.

NaCl (sodium chloride) is formed by the combination of a Na+ (sodium cation) and a Cl- (chloride anion). The sodium atom loses one electron to form a positively charged ion (cation), while the chlorine atom gains that electron to form a negatively charged ion (anion).

Thus, the correct answer is A) Na cation and Cl anion.

The valency of Calcium of 2+. Calcium has 2 electrons in its outermost shell, its electronic configuration being (2,8,8,2). In order to attain stability it loses 2 electrons to become stable according to the octet rule.

Ans: (c)

Solution: The correct pair of atom and its atomic symbol is Phosphorus -P