(c) Brass
     (d) Steel
Ans: (a)
283. Which one among the following most correctly determines the atomic number of an element? [NDA 2011]
     (a) Number of protons
     (b) Number of protons and electrons
     (c) Number of ions
     (d) Number of nucleons
Ans: (a)
284. The number of protons in a negatively charged atom (anion) is [NDA 2011]
     (a) more than the atomic number, of the element
     (b) less than the atomic number of the element
     (c) more than the number of electrons in the atom
     (d) less than the number of electrons in the atom
Ans: (d)
285. Helium is preferred to hydrogen in air balloons because it [UP PCS 2011]
     (a) is cheaper
     (b) is less dense
     (c) has greater lifting power
     (d) does not form an explosive mixture with air
Ans: (d)
286. Which one of the following pairs is correctly matched? [UP PCS 2011]
     (a) Silver iodide        : Horn Silver
     (b) Silver chloride      : Artificial rain
     (c) Zinc phosphide       : Rat poison
     (d) Zinc sulphide        : Philosopher"s wool
Ans: (c)
287. Match the following: [UP PCS 2011]
     List-I                   List-II
     A, Morphine              1. Antiseptic
     B. Sodium                2. Alloy
     C. Boric Acid            3. Analgesic
     D. German Silver         4. Kerosene oil
           A        B         C            D
     (a)   4        3         1            2
     (b)   2        4         3            1
     (c)   3        1         4            2
     (d)   3        4         1            2
Ans: (d)
288. Glycol is added to aviation gasoline because it [SSC Grad 2011]
                                                             405