Question Discussion & Solution

Given ten digit number is 6438123953

First half of the digits are : 64381

These are rearranged in descending order, so it becomes, 86431

Second half of the digits are : 23953

These are rearranged in ascending order, so it becomes, 23359

The new number is 8643123359

Comparing the new number with the given number

We see that, 4 digits position (highlighted) remains unchanged

Hence ‘4’ is the correct answer.

Rajendra Prasad is the first president of India. Similarly, the first president of USA is George Washington.

Hence, George Washington is the correct answer.

The correct answer is Sodium and potassium.

Key Points

• Sodium and Potassium metals are the two metals which are soft and can be cut with a knife.
  • Both belong to Alkali metals [first group of periodic table]
  • They are reactive metals.
  • As the atomic size increases down the group, so the force of attraction between the valence electron and nucleus decreases. 
  • Metallic bonds are not strong.
  • Potassium is softer than sodium.

Additional Information 

• Mercury- In a liquid state at room temperature, It is unique as a metal.
  • Mercury (Hg), also known as quicksilver.
  • Atomic Number- 80
• Zinc- Related to low Melting group.
  • Atomic Number- 30
  • Symbol- Zn
• Tin- It is a soft silvery-white metal with a bluish tinge.
  • Atomic Number- 50
  • Symbol- Sn

1 atm is equal to 760 torr.

• The atmospheric pressure(atm) is unit of the pressure within the atmosphere of Earth. 
• At sea level the Earth's atmospheric pressure is 1 atm.
• The torr is an absolute-scale which is unit of pressure.
• The unit took its name from Evangelista Torricelli, an Italian physicist and mathematician who invented the barometer theory in 1644.

Etymology is the study of origin of words; similarly Cosmology is study of origin of Universe.