Explanation

 Sound energy is a form of energy that can be heard by living beings.

Only those waves that have a frequency of 16 Hz to 20 kHz are audible to humans.

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

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

The epicenter of an earthquake is the point on the earth's surface vertically above the focus. Maximum damage is caused at the epicenter.

زلزلے کا مرکز زمین کی سطح پر عمودی طور پر اوپر کی حیثیت سے ایک نقطہ ہے۔ زیادہ تر نقصان زلزلے کے مرکز پر ہوتا ہے۔

Explanation

Pathology is the study of the causes and effects of disease or injury. 

Explanation

The first open-heart surgery in India was performed on February 16, 1961

By Dr. K.N. Dastur at BYL Nair Hospital in Mumbai.

He used a heart-lung machine developed with the help of engineers at the National Steel Company.

The surgery was performed on a 19-year-old girl named Hemlata 

Explanation

Benzene is an organic compound.

Molecular formula C3H3.

A benzene molecule is composed of six carbon atoms connected to a planar ring, each with a hydrogen atom.

Benzene is classified as a hydrocarbon because it contains only carbon and hydrogen atoms.

Empirical  Formula: C6H6

Explanation

Mangrove swamps serve all the following function

1.       Erosion protection for the coastline,

2.       Prevention of Typhoid and hurricane damage,

3.       Entrapment of sediment washed off land,

4.       Nursery for many aquatic organisms,

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Explanation

The stamen is the male reproductive organ.

It consists of a pollen anther and a long supporting filament.