Questions

The Sahara is the largest non-polar desert in the world. The Sahara is the largest hot desert and the third largest desert in the world after Antarctica and the Arctic.

The desert covers large sections of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia. It covers 9 million square kilometers (3,500,000 sq mi), amounting to 31% of Africa.

Its borders include the Mediterranean Sea to the north, the Atlantic Ocean to the west and the Red Sea to the east.

No work done as there is no external external pressure in free expansion. 

Hence, Work done in a free expansion process is Zero.

The main excretory organs of insects and spiders are Malpighian tubules.

Flag is called as Low order rigister & Accumulator is called as High order Rigister.

Bicycle is a compound machine in the above given options. A compound machine is a machine that is formed by two or more simple machines.

An eclipse happens when a planet or a moon gets in the way of the sun's light. Our planet Earth experiances two types of eclipses. They are Solar and Lunar eclipses.

Solar Eclipse : This occurs when The Sun, the Moon and the Earth are in a straight line. The moon being in middle blocks sun rays falling on the Earth.

Lunar Eclipse : The Sun, the Earth and the Moon are in a straight line. The Earth being in middle and moon in the shadow of Earth behind it.

Ans.  Suppose the speed of boat in still water is x km/h and speed of stream is y km/h

Speedof boat in downstream = (x + y) km/h x+ y = 32 …(i) 

Speed of boat in upstream = (x – y) km/h

x – y = 28 …(ii)

Add. Eqs. (i) and (ii), we get 2x = 60

x = 30 km/h

Metallic bond is a bond between two metal atoms. Here in the given option Hg is the only metal with metallic bond.