Science 2015 CBSE [Delhi] Set III

C_nH_2n–2 is the general formula for the alkyne series. The second member of the alkyne family is ethyne having formula C₂H₂.

The process of formation of new species due to evolution by genetic modification in the population of a pre-existing species is called speciation.

Biodegradable and non-biodegradable wastes should be discarded into two separate dustbins so that they are segrgated and recycled easily.

The following are the four characteristics of the images formed by convex mirrors:
1. The image formed by convex mirror is virtual and erect.
2. The image formed by convex mirror is always diminished.
3. When the object is placed anywhere between pole and infinity, the image is formed behind the mirror between the pole and foci of the mirror.
4. When the object is placed at infinity, the image is formed behind the mirror at foci.

The two advantages associated with water harvesting at community level are:

• The water collected during rainwater harvesting provide water to the vegetation and also improves the quality of ground water
• The underground stored rain water does not provide a breeding ground to mosquitoes and microorganisms.

i. One can reduce the use of electricity by switching off the lights and fans that are not in use.

ii. Plastic bottles of pickle and jam can be reused for storing things in the kitchen.

iii. One can recycle the electronic wastes by dismantling the items and using its components to make other items.

iv. Everyone should use paper instead of plastic for packing as paper can be reused and recycled.

When ethanol is heated at 443K with excess of conc. H₂SO₄ ethene(C₂H₄) is obtained.

In this reaction, sulphuric acid act as a dehydrating agent.

The process of adding hydrogen to an unsaturated compound is known as hydrogenation. For example, hydrogenation of ethyne:

Conditions for hydrogenation are:

i) An unsaturated compound

ii) A suitable catalyst

iii) A reactant molecule which is to be added to the unsaturated hydrocarbon

During hydrogenation of vegetable oils, liquid saturated fatty acids are converted into solid saturated fatty acids.

(i) Among the given elements, ₁₉K has one electron in the outermost shell as its electronic configuration is 2, 8, 8, 1.

(ii) The elements ₄Be and ₂₀Ca belong to the same group, i.e., Group 2 as both elements have two electrons each in their outermost shells.

Electronic configuration of ₄Be = 2, 2.
Electronic configuration of ₂₀Ca = 2, 8, 8, 2.

(iii) The atomic number of element X = 17
Electronic configuration of element X = 2, 8, 7.
Number of valence electrons in X = 7
Valency of X = 8 − 7 = 1

Similarly, Atomic number of element K = 19

Electronic configuration of K is 2, 8, 8, 1.
Number of valence electron in K = 1
Valency of K = 1

Therefore, on combining the elements K and X, we get the formula of compound as KX.

The compound KX is of ionic nature.

There are seven periods in modern periodic table.

Metallic character decreases from left to right in a period, while the valency first increases from 1 to 4 and then decreases to zero.

Atomic size increases down the group, whereas, valency remains same.