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: B) Half year Explanation: 3300 ----- 3% ↑ (1st time interval, 99) → 3399. Here, time interval is given as half-yearly i.e. 6 months.

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) 3/4 hrs Explanation: Walking at 3/4th of usual rate implies that time taken would be 4/3th of the usual time. In other words, the time taken is 1/3rd more than his usual time   so 1/3rd of the usual time = 15minor usual time = 3 x 15 = 45min = 45/60 hrs = 3/4 hrs.

Answer: A) 10 days Explanation: After 10 days, the remaining food would be sufficient for the 1000 students for 20 more days -->If 1000 more students are added, it shall be sufficient for only 10 days (as the no. of students is doubled, the days are halved).

Answer: B) 2 Explanation: Given a2 + b2 = c2   Now  1logc+ab  + 1logc-ab    = logbc+a + logbc-a   = logbc2-a2 = 2logbb = 2

Answer: D) 44 & 28 Explanation: Letx = peacocks y = deers 2x + 4y = 200 x + y = 72 y = 72 - x 2x + 288 - 4x = 200 x = 44 peacocks y = 28 deers

Answer: C) Backup file Explanation: In computing, ".bak" is a filename extension commonly used to signify a backup copy of a file.