Explanation

Sodium carbonate is also known as washing soda.

It is commonly used to remove permanent hardness from water.

It reacts with calcium and magnesium ions, which are the causes of permanent hardness, to form precipitates that can be removed from the water.

Explanation

Water is neutral and does not have a taste.

The taste buds on our tongues can detect five basic tastes: sweet, sour, salty, bitter, and umami (savory).

Water does not contain any molecules that stimulate these taste buds, making it tasteless.

Explanation

Temporary hardness is caused by:

• Calcium bicarbonate — Ca(HCO₃)₂
• Magnesium bicarbonate — Mg(HCO₃)₂
• Release Ca²⁺ and Mg²⁺ in water.
• Removed by boiling → form insoluble CaCO₃, MgCO₃.
• Permanent hardness (sulfates/chlorides) can't be removed by boiling.

Explanation

The permanent hardness of water is due to the presence of MgSO₄ (magnesium sulfate).

Permanent hardness is caused by dissolved minerals like calcium sulfate (CaSO₄) and magnesium sulfate, which cannot be removed by boiling the water.

Explanation

Polio is also known as poliomyelitis.

It is a disease caused by the poliovirus.

The virus is usually spread through the fecal-oral route, which includes through contaminated water and food.

Explanation

The bottom of the stratosphere is around 10 km (6.2 miles or about 33,000 feet) above the ground at middle latitudes.

The top of the stratosphere occurs at an altitude of 50 km (31 miles).

Explanation

The composition of dry air is:

1. Nitrogen (N2) - approximately 78.08% by volume
2. Oxygen (O2) - approximately 20.95% (21%) by volume
3. Argon (Ar) - approximately 0.93% by volume
4. Carbon Dioxide (CO2) - approximately 0.04% by volume (varies with location and time)

Explanation

Oxygen (O2) is not a greenhouse gas.

Greenhouse gases are gases in the Earth's atmosphere that absorb and emit radiation, trapping heat and contributing to the Greenhouse Effect.

The main greenhouse gases are:

• Carbon dioxide (CO2)
• Methane (CH4)
• Nitrous oxide (N2O)
• Water vapor (H2O)
• Ozone (O3)
• Chlorofluorocarbons (CFCs)
• Hydrofluorocarbons (HFCs)
• Perfluorocarbons (PFCs)

Explanation

The tropopause is the layer that separates the stratosphere and troposphere.

It's a boundary layer located at an average altitude of around 12 km (7.5 miles) above the Earth's surface, where the troposphere ends and the stratosphere begins.

Explanation

Atmospheric pressure decreases as altitude increases.

As you go higher, the air pressure decreases because there are fewer air molecules above you, exerting less pressure.

This is why aircraft pilots must adjust their altimeters to account for changes in air pressure as they ascend or descend.