(Each and every questions are not answered, they will be added soon and in any chaos please comment)

1     The ability of an atom in a covalent bond to attract electrons to itself is called its electronegativity.

     The greater the difference between the electronegativities of the two atoms in the bond, the more

     polar is the bond.

     Which pair will form the most polar covalent bond between the atoms?

     A     chlorine and bromine

     B     chlorine and iodine

     C     fluorine and chlorine

     D     fluorine and iodine

Solution:

The sequence of electro negativity is F>O>N>Cl>Br>I

Hence, it becomes apparent that option D is the best choice as the most electronegative compound (F) attracts the least electro negativity element of the series.

Solution:

When temperature increases the kinetic energy possessed by the molecules also increase and more molecules have the activation energy. As a result, the graph peak shifts toward right and has less height. (C and D are incorrect)

In graph A and B, A is not accurate as the curve does not originate from origin.

The answer is B.

Solution:

Bond formation is exothermic and bond break down is exothermic.  So we need to know what kinds of bonds are broken and what sort of bonds are formed. The easiest way to do it is to draw the displayed formula of the reactants and products and sum up all the bond energy of reactant and product side and the value of reactant side is positive but of product side is negative. And, add them up.

In this case, the total endothermic bond energy is:  +1077+(2*436)=+1949

Total exothermic bond energy is :-(3*410)-(360)-(460)=-2050

Enthalpy change= +1949-2050=-101 KJ/mol

The answer is B

7    Flask X contains 5 dm3 of helium at 12 kPa pressure and flask Y contains 10 dm3 of neon at 6           kPa pressure.

      If the flasks are connected at constant temperature, what is the final pressure?

     A     8 kPa              B    9 kPa              C     10 kPa            D     11 kPa

Solution:

For X, PV=nRT

Or, n=PV/ (RT)

Or, n=60/ (RT)

Similarly for Y,

n=60/ (RT)

When the flask are joined,

PV=nRT

Or, P*(5 + 10) *10^-3= { 60/ (RT) + 60/ (RT) } * RT

Or, P=8000

Hence, the answer is A

10    Which molecule or structure does not contain three atoms bonded at an  angle between  109° and 110°?

     A     ethanoic acid

     B     graphite

     C     propane

     D     silicon(IV) oxide

Solution:

Initially make the displayed formula of the listed compounds.

In Ethanoic acid and propane, the carbon atom is bonded to four Hydrogen making it a perfect tetrahedral which have bond angle of 109.5. (A and C incorrect)

In silicon oxide, one silicon atom is bonded to four oxygen atom and hence has bond angle of 109.5 degree. (D is incorrect)

In graphite, one carbon atom is bonded to just three other carbon atoms hence, it has the bond angle of roughly 120 degree.

The answer is B 

Solution:

One mole of X forms 2 mole of Y. let’s assume that the volume is 1 dm3 (assumption of it makes the calculation easier as concentration becomes equal to no. of moles). When equilibrium is established the no. of moles of X decreases from 0.50 moles to 0.25 moles, it implies that 0.50(0.25*2) moles of Y is formed. Hence, the value of Kc is

Kc=[Y]^2/[X]

  =0.50^2/0.25

  =1      (B and D are incorrect)

When the concentration of X is 0.25, concentration of Y is 0.50, which is shown in graph C and D.

Since D can’t be right), C is right answer.

Solution:

The temperature required to decompose the carbonates of group 2 increases when going down the group (due to polarization). Hence, Sr has more Td than Mg. (A and B are incorrect)

The residue of the reaction i.e. MgO and SrO are then reacted with water. The solution of Mg(OH)2 is weakly alkaline but Sr(OH)2 is comparatively stronger. Hence has high pH value.

So, the answer is D.

20    How many structural isomers are there of trichloropropane, C3H5Cl3? 

     A     3                  B     4                 C     5                  D     6 

 Solution:

The most easy way to solve the question is to put Cl at various positions. Since there are three chlorines you have five ways to do that as you can place on Cl on following positions 1,1,1 or 1,1,2 or 1,2,1 or 1,2,2 or 1,2,3.

So the answer is C

(Note: Be vigilant in 1 and 3 no. carbons. Sometime, you can get confused as they can get similar)

21    Nine compounds have molecular formula C4H8Br2 . 

     Which compound may be synthesised from an alkene by an addition reaction? 

     A     1,1-dibromobutane 

     B     1,2-dibromobutane 

     C     1,3-dibromobutane 

     D     1,3-dibromomethylpropane 

Solution:

Br can only get added to adjacent carbons who have double bond .

In the answer options you can see all compound have Br added to 1 no. carbon (other no. can differ). So, it is wise to draw a structural formula in which double bond is between  1 and 2 no. carbon i.e.

CH3─CH2─CH=CH2, when this butene reacts with Br2, the double bond gets broken and each carbon atom can another bond. But, only 1 and 2 no. carbon can form the bond , rest all carbon atoms have already four bonds. (C and D are incorrect)

And, 1 no. carbon has already three bonds (2 with H and one with C). hence, 2 Br cant get added to it (A is incorrect, instead the two Br gets added to the 1 and 2 no. carbon atoms.

B is the right answer.