A periscope is an optical instrument that uses a system of prisms, lenses, or mirrors to reflect images through a tube.

Light from a distant object strikes the top mirror and is then reflected at an angle of 90 degrees down the periscope tube. At the bottom of the periscope, the light strikes another mirror and is then reflected into the viewer’s eye.

Hence, A periscope works by the principle of Total internal reflection.

In chemistry, a metal is an element that readily forms positive ions (cations) and has metallic bonds. Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances.

Examples of metals are aluminium, copper, iron, tin, gold, lead, silver, titanium, uranium, and zinc.

Here Se - Selenium is an element but is not a metal, S - Sulphur is not a metal and I - Iodine is also not a metal.

Hence, Zn - Zinc is the only metal in the given options.

In a brief, the system software is the interface between the hardware and user applications. System software is a type of computer program that is designed to run a computer’s hardware and application programs.

Examples : OS, System utilities, BIOS like mouse, keyboard, hard disc, Device drivers, Assembler,...

When the European union formed nations began to cooperate on law enforcement. The European Union is set up with the aim of ending the frequent and bloody wars between neighbours, which culminated in the Second World War.

As of 1950, the European Coal and Steel Community begins to unite European countries economically and politically in order to secure lasting peace. The six founding countries are Belgium, France, Germany, Italy, Luxembourg and the Netherlands. The 1950s are dominated by a cold war between east and west.

The historical roots of the European Union lie in the Second World War. Europeans are determined to prevent such killing and destruction from ever happening again.

The reason why drunk people acts like stupids is when they drink, especially if they drink a lot, first their brain becomes impaired by such large quantities of alcohol that it cannot operate properly. So they cannot judge anything.

Hence, Alcohol first impairs your Judgement.

I am ABBREVIATION.

Yes, i make things short and asks the full form of that thing.

Ex : FCI - Food Corporation of India

IAS - Indian Administrative Service.

A Shrimps heart is located on its head.

1. How to find Speed(s) if distance(d) & time(t) is given:

 Speed (S) = Distance (D)Time (T) 

Ex: Find speed if a person travels 4 kms in 2 hrs?

Speed = D/T = 4/2 = 2 kmph.

2.  Similarly, we can find distance (d)  if speed (s) & time (t) is given by

Distance (D) = Speed (S) x Time (T)

Ex : Find distance if a person with a speed of 2 kmph in 2 hrs?

Distance D = S X T = 2 x 2 = 4 kms. 

3.  Similarly, we can find time (t) if speed (s) &  distance (d) is given by

Time (T) = Distance (D)Speed (S)

Ex : Find in what time a person travels 4 kms with a speed of 2 kmph?

Time T = D/S = 4/2 = 2 hrs.

4. How to convert  km/hr into m/sec :

P km/hr = P x 518 m/sec

Ex : Convert 36 kmph into m/sec?

36 kmph = 36 x 5/18 = 10 m/sec 

5. How to convert  m/sec into km/hr :

P m/sec = P x 185 kmph.

Ex : Convert 10 m/sec into km/hr?

10 m/sec = 10 x 18/5 = 36 kmph.

6.  If the ratio of the speeds of A and B is a:b, then the ratio of the times taken by them to cover the same distance is b : a.

7.  Suppose a man covers a certain distance at x km/ hr and an equal distance at y km/hr . Then, the average speed during the whole journey is 2xyx+y km/hr.