Explanation

The fundamental units in the SI (International System of Units) are:

1. The meter (m) for length,
2. The kilogram (kg) for mass,
3. The second (s) for time,
4. The ampere (A) for electric current,
5. The kelvin (K) for thermodynamic temperature,
6. The mole (mol) for the amount of substance, 
7. The candela (cd) for luminous intensity.

These seven base units are independent and form the foundation of the SI system, from which all other units are derived. 

Explanation

A hygrometer is an instrument used to measure relative humidity.

Humidity is the measure of the amount of moisture in the air.

A psychrometer is an example of a hygrometer.

Explanation

The initial setting of cement is caused by:

• Hydration of Tricalcium Aluminate (C₃A).
• Reaction of C₃A with water, which starts rapidly after mixing.
• Formation of calcium aluminate hydrates, causing the paste to stiffen.
• Gypsum is added to slow down this reaction and prevent flash setting.

Explanation

Periscopes allow a submarine, when submerged at a relatively shallow depth, to search visually for nearby targets and threats on the surface of the water and in the air.

When not in use, a submarine's periscope retracts into the hull.

Explanation

Quantum numbers describe values of conserved quantities in the dynamics of a quantum system

Explanation

A protein is a naturally occurring, extremely complex substance that consists of amino acid residues joined by peptide bonds. Proteins are present in all living organisms and include many essential biological compounds such as enzymes, hormones, and antibodies.

Explanation

Explanation

Found in many foods including yeast, cereal grains, beans, nuts, and meat

Water soluble 

Explanation

Seismic waves are waves of energy that travel through Earth's layers

 result of  volcanic eruptions.

 large landslides and large man-made explosions that give out low-frequency acoustic energy.

Explanation

 Common salt comprises sodium and chlorine.

Sweat consists of about 99% water,

0.2-0.5% salts mainly sodium chloride

and traces of urea (0.08%).