(a) All bases are alkalis
     (b) None of the bases is alkali
     (c) There are no more bases except the alkalis
     (d) AII alkalis are bases but all bases are not alkalis
Ans: (d)
276. Which one among the following statements about an atom is not correct? [CDS 2012]
     (a) Atoms always combine to form molecules
     (b) Atoms are the basic units from which molecules and ions are formed
     (c) Atoms are always neutral in nature
     (d) Atoms aggregate in large numbers to form the matter that we can see, feel and touch
Ans: (a)
277. The macro-nutrients provided by inorganic fertilizers are [CDS 2012]
     (a) carbon, iron and boron
     (b) magnesium, manganese and sulphur
     (c) magnesium, zinc and iron
     (d) nitrogen, phosphorus and potassium
Ans: (d)
278. Which one among the following nontoxic gases helps in formation of enzymes which ripen fruit? [CDS 2012]
     (a) Acetylene
     (b) Ethane
     (c) Methane
     (d) Carbon dioxide
Ans: (a)
279. Age of fossil may be found out by determining the ratio of two isotopes of carbon. The isotopes are [CDS 2012]
     (a) C-12 and C-13
     (b) C-13 and C-14
     (c) C-12 and C-14
     (d) C-12 and carbon black
Ans: (c)
280. The major component used in preparation of different types of glasses is [NDA 2011]
     (a) Silica
     (b) Sodium borate
     (c) Calcium silicate
     (d) Sodium silicate
Ans: (a)
281. The main constituent of vinegar is [NDA 2011]
     (a) Citric acid
     (b) Acetic acid
     (c) Ascorbic acid
     (d) Tartaric acid
Ans: (b)
282. Which one among the following is not a mixture? [NDA 2011]
     (a) Graphite
     (b) Glass
                                                             404