Answer: A) 1/3 Explanation: In a family with 2 children there are four possibilities:1) the first child is a boy and the second child is a boy (bb)2) the first child is a boy and the second child is a girl (bg)3) the first child is a girl and the second child is a boy (gb)4) the first child is a girl and the second child is a girl (gg) But already given that one child is boy. So we have three possibilities of (bb)(bg)(gb).n(E)= both are boys=BB=1n(S)= 3Required probability P = n(E)/n(S) = 1/3.

Answer: A) the mass of the liquid displaced Explanation: Buoyancy or Upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid.

Answer: C) 6 days Explanation: From the given data, 12 children 16 days work,One child’s one day work = 1/192. 8 adults 12 days work,One adult’s one day’s work = 1/96. Work done in 3 days = ((1/96) x 16 x 3) = 1/2 Remaining work = 1 – 1/2 = 1/2 (6 adults+ 4 children)’s 1 day’s work = 6/96 + 4/192 = 1/12 1/12 work is done by them in 1 day. 1/2 work is done by them in 12 x (1/2) = 6 days.

Polarity ::  The polarity of a molecule defines its other physical properties such as melting point, boiling point, surface tension, vapor pressure etc... Simply, polarity occurs when the electron distribution in a molecule is asymmetric. This results in a net dipole moment in the molecule. One end of the molecule is charged negative while the other gets a positive charge.   The polarization of a molecule greatly depends on the shape of the molecule. A diatomic molecule like HF mentioned above has no issue of shape. The net dipole moment is only due to the uneven distribution of electrons between the two atoms. However, when there are more than two atoms involved in making a bond, there are many complexities.   The water molecule is of bent shape. Therefore, when the two pair of electrons shared by oxygen with two hydrogen atoms is pulled towards oxygen, the net dipole moment results in the direction of the oxygen atom. There is no other force to cancel out the resultant dipole moment. Hence, the water molecule is highly polar.   Ammonia molecule is of a pyramid shape and the electronegative N atom pulls the electrons towards itself. The three N-H bonds are not in the same plane; hence the dipole moments created do not get canceled out. This makes ammonia a polar molecule.   However, the dipole moments sometimes get canceled due to the shape of the molecules, making the molecule non-polar. Carbon dioxide is such a molecule.

Answer: D) 31.68 years Explanation: We know that 1 year = 365.25 days 1 day = 24 hours 1 hour = 60 minutes 1 minute = 60 seconds   => 1 Year = 365.25 x 24 x 60 x 60 Seconds But 1 billion seconds = ? 1 Year = 365.25 x 24 x 60 x 60 Seconds     ?     =  1000000000 Seconds   ? = 1000000000365.25 x 24 x 60 x 60 years = 31. 68 years.

Answer: C) 48.4 % Explanation: Let marked price = Rs. 100. Then, C.P. = RS. 54, S.P. = Rs. 85Gain % = 31/64 x 100 = 48.4%.

Answer: A) H and Br Explanation: Only H and Br form Polar Covalent Bond.   Covalent bonding: Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability. 1. Polar Covalent Bond 2. Nonpolar Covalent Bond   1. Polar Covalent Bond: A Polar Covalent Bond is created when the shared electrons between atoms are not equally shared. This occurs when one atom has a higher electronegativity than the atom it is sharing with. The atom with the higher electronegativity will have a stronger pull for electrons (Similiar to a Tug-O-War game, whoever is stronger usually wins). As a result, the shared electrons will be closer to the atom with the higher electronegativity, making it unequally shared.   2. Nonpolar Covalent Bond: A Nonpolar Covalent Bond is created when atoms share their electrons equally. This usually occurs when two atoms have similar or the same electron affinity. The closer the values of their electron affinity, the stronger the attraction. This occurs in gas molecules; also known as diatomic elements. Nonpolar covalent bonds have a similar concept as polar covalent bonds; the atom with the higher electronegativity will draw away the electron from the weaker one.   Here H and H and N and N form Non-polar covalent bonds. Na and Br form the ionic bond.

Answer: B) 12.5% Explanation: Here to convert 0.125 into % First convert to fractio Multiply and divide by 1000 => 0.125 x 10001000 = 1251000 = 18 => Now, in percentage18 x 100 = 12.5%