Answer: C) 042 Explanation: From all the hints given,  only 042 satisfies and it unlocks the key.

Answer: C) Glass Explanation: Sound is a mechanical vibration and needs a medium for propagation. The higher the density of the medium, the faster the sound travels. So, sound cannot travel through vacuum.   As the sound travels faster in solids than liquids and gases, sound travels faster in the glass than Air and water.

Answer: B) 12.5% Explanation: Let p% of a day is 3 hrs. We know that a day has 24 hrs. => p x 24/100 = 3 => p = 300/24 => p = 12.5%   Hence, 3 hrs is 12.5% of a day.

Answer: C) 6! x ⁷P₆ Explanation: We can initially arrange the six boys in 6! ways.Having done this, now three are seven places and six girls to be arranged. This can be done in ⁷P₆ ways. Hence required number of ways = 6! x ⁷P₆

Answer: C) Covalent Explanation: Covalent type of bonding joins the two hydrogen atoms. Hydrogen atoms in compounds such as H2 and H2O are joined to the molecule with covalent bonds. This is where electrons are shared between the atoms in order to fill there valence shells.

Answer: D) 2.25 % Explanation: SP of each car is Rs. 404415, he gains 15% on first car and losses 15% on second car. In this case, there will be loss and percentage of loss is given by = [(profit%)(loss%)]/100 = (15)(15)/100 % = 2.25%

Answer: B) 3:2:4 Explanation: Given, y/(x - z) = (y + x)/z = x/yyz = xy + x2 - yz - xz ....(1)Also xy = yx-z ⇒x2 -xz = y2 ....(2)Using (1) and (2), we get yz = xy - yz + y22yz = xy + y22z = x + y Only option (B) satisfies the equation.

Answer: D) Peat Explanation: The first of the four stages of coal formation is lignite coal.   There are four stages of coal formation:   1. Peat,   2. Lignite,   3. Bituminous and   4. Anthracite. The bacteria has removed a large portion of the other constituents of the plant matter and left around 25 to 34 percent.