Question

give reasons for all the questions​

Answer 1

Answer:

(1) noble gases are non-reactive in nature hence do not combine with other elements to form molecules.

(2)(dil) nitric acid cannot be used in the preparation of hydrogen because it is a good oxidizing agent and hence oxidizes hydrogen formed to give water a a product.

(3)Even though hydrogen is lighter than air it is not collected by downward displacement of air because of these reasons:

Hydrogen  gets oxidized when it is exposed to oxygen which makes it burn with a pale blue flame and the residue is water. This means that it mixes with oxygen.  

Downward displacement of air requires a gas that does not mix with air and is lighter than air. Hydrogen is lighter than air but mixes with air.

(4)As calcium carbide  is a deliquescent substance it absorb water from the atmosphere when exposed to air. If anhydrous calcium chloride is exposed in the air it will also absorb water from the atmosphere and turn into a colourless solution.

hope it helps

Answer 2

Answer:

(i) Noble gases already have an octet( eight electrons in outermost shell) in their outermost shell i.e..they are already in a stable form .

(ii)Dilute nitric acid is a powerful oxidizing agent, and the oxygen formed due to decomposition oxidizes the hydrogen to give water, thus defeating the purpose of the reaction

3Zn+8HNO3 ------->3Zn(NO3)2+4H2O+2NO

(iii)It forms an explosive mixture with air and therefore cannot be collected by downward diaplacement of air

(iv)As calcium carbide is a deliquescent substance it absorbs water from atmosphere.Henceforth if calcium chloride is exposed to air it will form water,a colourless solution

Hope this helped......