Answer: B) Oxygen Explanation: Rust forms when oxygen reacts with chemicals in rocks, and that is often the case with many other elements in general. Like a copper nail being exposed to the air will rust.

Answer: C) Steel Explanation: The primary use of iron ore is in the production of iron. Most of the iron produced is then used to make steel. Steel is used to make automobiles, locomotives, ships, beams used in buildings, furniture, paper clips, tools, reinforcing rods for concrete, bicycles, and thousands of other items.

Answer: D) 5 Explanation: By trial and error method, we get2880/3 = 960 is not a perfect square2880/4 = 720 is not a perfect square2880/5 = 576 which is perfect square of 24Hence, 5 is the least number by which 2880 must be divided in order to make it into a perfect square.

Answer: A) 788 Explanation: (kx22)/100 = 340 - 166.64 = 173.36 k = (173.36 x 100)/22 k = 788

Answer: C) +4 Explanation: The given compound is NaHCO3 Sodium bicarbonate which is commonly known as Baking soda. Oxidation numbers are the charges on ions. When a neutral atom loses electrons it becomes positively charged. When a neutral atom gains electrons it becomes negatively charged.   Here the C represents the oxidation state of carbon in this compound. Compounds are electrically neutral, which is why we set the sum of the oxidation states equal to zero. Sodium has a +1 oxidation state. Hydrogen has a +1 oxidation state. Oxygen has a -2 oxidation state. There are three oxygen atoms, which means the total oxidation state provided by both oxygen ions is -6. Adding up these oxidation states we get: 1 + 1 + (-6) + C = 0 -4 + C = 0 => C = 4 This means the oxidation state of carbon in this compound is +4.

Answer: D) 140 mts Explanation: Speeds of two trains = 30 kmph and 58 kmph => Relative speed = 58 - 30 = 28 kmph = 28 x 5/18 m/s = 70/9 m/s Given a man takes time to cross length of faster train = 18 sec   Now, required Length of faster train = speed x time = 70/9  x  18 = 140 mts.

Answer: B) 9 Explanation:   Here in 2nd column if you add the individual digits  we get  3 + 7 + 0 =10 , 2 + 2 + 4 = 8 , 7 + 3 + 0 = 10   7   10   3  --> 7+3 =10   6   8     2  --> 6+2 =8   x   10   1  --> x+1 =10   Here we can observe that by adding 1st and 3rd column elements we get 2nd column elements  --> x = 9