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⁞ Chemistry

General Science ➤ Chemistry ➤ Miscellaneous
Question 6
Q6.  Which one among the following is not a chemical change? [NDA/NA 2013]
 

Answer :  Evaporation of water


Evaporation of water is not a chemical change.

The evaporation of water is a physical change. When water evaporates, it changes from the liquid state to the gas state, but it is still water; it has not changed into any other substance. For example, hydrogen burning in air undergoes a chemical change in which it is converted to water.
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Question 7
Q7.  A molecule of a substance is similar to its atom for [SSC Multitasking 2013]
 

Answer :  monoatomic molecule


A molecule of a substance is similar to its atom for monoatomic molecule.
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Question 8
Q8.  Who is the founder of quantum theory of radiation? [SSC CGL 2013]
 

Answer :  Planck


Max Planck is the founder of quantum theory of radiation.

max-planck
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Question 9
Q9.  What are the elements which are liquids at room temperature and standard pressure?

I. HeliumII. Mercury
III. ChlorineIV. Bromine
Select the correct answer using the codes given below. [CDS 2013]
 

Answer :  II and IV


There are two elements that are liquid in room temperature.

Bromine (Br) melts at 265.9 K
Mercury (Hg) melts at 234.32 K - This is very interesting because all of Mercury's neighboring elements are solids at room temperature. Mercury is also much less reactive than Cadmium and Zinc which are directly above Mercury. Mercury doesn't conduct heat or electricity as well as other members of its group. Most metals are solids at room temperature because they share their valence electrons with surrounding metal atoms. However Mercury hangs onto its 6 valence electrons tighter than any other atom. Thus Mercury-Mercury bonds are weaker compared to other metal-metal bonds. It is also the only metal that doesn't form diatomic molecules in the gas phase. Since the amount of heat required to overcome the weak Mercury-Mercury bonds is lower, Mercury melts and boils at very low temperatures.

There are four elements that melts slightly above the room temperature.
Francium (Fr) melts at 300 K
Cesium (Cs) melts at 301.59 K (fun fact - Cesium has the largest atoms. Cs atoms are about 30pm larger than Rubidium atoms)
Gallium (Ga) melts at 303.3 K
Rubidium (Rb) melts at 312.46 K
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