Explanation

• Brass gets discoloured in air due to Hydrogen Sulphide (H₂S).
• This gas reacts with the copper in brass to form a dark layer of copper sulphide, giving it a tarnished appearance.

Additional information:

• Tarnishing is superficial and can be cleaned using polishing or chemical cleaners.
• This phenomenon is also called sulphide tarnishing.

Last verified on 17-01-2026

Explanation

Explanation

• Electron: Discovered by J. J. Thomson, 1897

Additional information:

• Proton: Discovered by Ernest Rutherford, 1919
• Neutron: Discovered by James Chadwick, 1932
• Atomic Model Proposed: Plum Pudding Model
• Significance: First subatomic particle discovered

Last updated by NA on 05-11-2026

Explanation

Aluminum is a metal that can be recycled many times without losing its properties.

Additional information:

• Recycling 1 ton of aluminum saves up to 95% of the energy required to make new aluminum.
• Aluminum is widely used in cans, foils, and packaging, making it highly recyclable.

Last verified on 16-01-2026

Explanation

Dynamite was invented by Alfred Nobel in the 1860s.

Additional Information REKATED ALFRED NOBEL

He was a chemist from Sweden.

Full name: Alfred Bernhard Nobel

Born: October 21, 1833, Stockholm, Sweden

The founder of the Nobel Prize

Invented Nitro-glycerine in 1875.

Died: on December 10, 1896, in Sanremo, Italy

Explanation

A mixture of two or more metals (or a metal with non-metals) is called an alloy

An alloy is made by mixing metals.

It improves strength and durability.

Steel (iron and carbon), is an example of an alloy.

Explanation

Heavy water (D₂O) is used as a moderator because it slows neutrons without absorbing them much.

A moderator slows down fast neutrons in a nuclear reactor.

Slower neutrons help sustain the fission chain reaction.

Pakistan’s nuclear reactors commonly use heavy water as a moderator.

Explanation

Nuclear fission is the splitting a heavy nucleus into smaller nuclei. 

The word "fission" means splitting, so in nuclear fission, a large, unstable nucleus is split apart into smaller nuclei, releasing energy in the process. 

Explanation

Francium is extremely rare because it is highly radioactive and decays very quickly.

Only tiny trace amounts exist naturally in the Earth’s crust at any given time.

Explanation

When burned, copper produces a blue-green flame due to excited copper ions.

This color is commonly used in flame tests to identify copper.