Explanation

Radon (Rn) is a radioactive gas formed from the decay of uranium and radium found in rocks and soil.

He (Helium): Helium is present in trace amounts in the atmosphere.

Ne (Neon): Neon is also present in trace amounts in the atmosphere.

Ar (Argon): Argon is the most abundant noble gas in Earth's atmosphere, making up about 0.93% of the air. 

Explanation

The concept of the covalent bond was introduced by G.N. Lewis in 1916.

Through his electron dot structure theory.

He explained that atoms share electron pairs to achieve stable electronic configurations (octet rule).

Explanation

Zinc (Zn) has an atomic number of 30.

Its standard atomic weight is 65.38 u.

This value is taken from the IUPAC periodic table.

It represents the average mass of naturally occurring isotopes of zinc.

Explanation

• An exothermic reaction releases energy into the surroundings as heat or light.
• Heat released: Energy moves outward.
• Surroundings warm: Temperature rises.
• Negative enthalpy: Delta H < 0
• Lower product energy: Reactants hold more energy.

Additional information:

• In an endothermic reaction, heat is absorbed from the surroundings.
• Examples include photosynthesis and melting of ice.

Explanation

The molar mass of Ca in CaCO₃ is 40 out of 100.

Hence, calcium makes up 40% of CaCO₃.

The molar mass of CaCO₃ is approximately 100 g/mol.

The molar mass of calcium (Ca) in CaCO₃ is about 40 g/mol.

The proportion of calcium in CaCO₃ is  40/ 100 = 0.4

Therefore, in 0.1 g of CaCO₃, the amount of calcium is  0.1×0.4=0.04 g.

Explanation

Plaster of Paris (POP) is calcium sulfate hemihydrate (CaSO₄·½H₂O).  

It is made by heating gypsum (CaSO₄·2H₂O) to remove water partially.

Explanation

The chemical symbol C represents Carbon.

It is a non-metal element.

It is the basis of organic compounds and essential for all living organisms.

Explanation

When two or more atoms chemically bond together, they form a molecule.

Examples include H₂ (hydrogen molecule) and O₂ (oxygen molecule).

Explanation

• The 4th and 5th periods in the periodic table are known as the long periods.
• These periods contain 18 elements each, making them the longest periods in the periodic table.

Important Points:

• Short periods: 1st and 2nd periods (2 and 8 elements, respectively)
• Long periods: 4th and 5th periods (18 elements each)
• Normal periods: 3rd and 6th periods (8 and 12 elements, respectively)

Explanation

Fertilizers rich in nitrogen are called nitrogenous fertilizers (e.g., urea, ammonium nitrate).

They are mainly used to promote leafy and vegetative growth in plants.