Answer: A) the existence of unpaired electrons in the valence shell Explanation: When atoms react they do so in order to reach the lowest energy, which is the most stable. The electrons orbitals will overlap in the way that reduces the energy the most. Orbitals of similar energy will produce the greatest stabilisation.The answer you gave isn't the whole story, it depends what species is reacting with what. The effective nuclear charge on the atom will affect the energy of the valance electrons.   Hence, the reactivity of an atom arises from the existence of unpaired electrons in the valence shell.

Answer: A) 15 Explanation: Two series alternate here, with every third number following a different pattern.In the main series, 4 is added to each number to arrive the next.In alternate series, 5 is subtracted from each number t arrive the next number.Here in the main series 3 + 4 = 77 + 4 = 1111 + 4 = 1515 + 4 = 19 In alternate series 24 - 5 = 1919 - 5 = 14...

Answer: A) long, double chains of nucleic acids. Explanation: Gene is a segment of chromosomal DNA or a sequence of DNA or RNA that codes for a molecule that has a function. It is the basic physical and functional unit of heredity.   As genes are made up of DNA it impies that they are long, double chains of nucleic acids as DNA is made of nucleic acids.

Answer: A) 600 Explanation: Two men, three women and one child can be selected in ⁴C₂ x ⁶C₃ x ⁵C₁ ways = 600 ways.

Answer: B) 40 yrs Explanation: Let the present ages of Ajay and Vijay be 'A' and 'V' years respectively. => A - 8 = 4/3 (V - 8) and A + 8 = 6/5 (V + 8) => 3/4(A - 8) = V - 8 and 5/6(A + 8) = V + 8 V = 3/4 (A - 8) + 8 = 5/6 (A + 8) - 8 => 3/4 A - 6 + 8 = 5/6 A + 20/3 - 8 => 10 - 20/3 = 10/12 A - 9/12 A => 10/3 = A/12 => A = 40.

Answer: A) Musician Explanation: An actor performs in a play. A musician performs at a concert. Choices b, c, and d are incorrect because none is people who perform.   Hence, Play is to actor as concert is to Musician.

Answer: D) 15 × 13 × 13! Explanation: 15! - 14! - 13! = (15 × 14 × 13!) - (14 × 13!) - (13!) = 13! (15 × 14 - 14 - 1) = 13! (15 × 14 - 15) = 13! x 15 (14 - 1) = 15 × 13 × 13!

Answer: D) Wednesday Explanation: Here from 4th December 1999 to 3rd January 2000,there is a difference of 30 days.Number of odd days = 30/7 = 2 odd days Then no. of odd days = 2 => tuesday and wednesday(from monday). Hence on 3rd january it is wednesday.