#ssc 10th
- The froth floatation method is mainly used to concentrate Answer: C. sulphide ores Sulphide ore particles are wetted by oil and rise with the froth, while gangue is wetted by water and sinks. 1
- Heating a sulphide ore strongly in excess of air is called Answer: B. roasting Roasting converts a sulphide ore into its oxide, e.g. 2ZnS + 3O₂ → 2ZnO + 2SO₂ . Calcination is heating in limited or no... 1
- An alloy in which one of the metals is mercury is called Answer: A. an amalgam Any alloy of mercury is called an amalgam. 1
- Bronze is an alloy of Answer: C. copper and tin Bronze is copper and tin; brass is copper and zinc. 1
- In the extraction of aluminium by electrolytic reduction of alumina, cryolite and fluorspar are added to Answer: D. lower the melting point of the mixture and increase its conductivity Alumina melts above 2000 °C. Cryolite and fluorspar lower th... 1
- Which of the following metals does not react with dilute hydrochloric acid? Answer: A. Copper Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids. 1
- Coating iron with a thin layer of zinc to prevent corrosion is called Answer: C. galvanizing Galvanizing is coating iron or steel with zinc; tinning is coating with tin. 1
- In Dobereiner's triad lithium (7), sodium and potassium (39), the approximate atomic mass of sodium is Answer: C. 23 The middle element's atomic mass is about the mean of the other two: 7 + 39/2 = 23 . 1
- The number of groups in the modern periodic table is Answer: A. 18 The modern periodic table has 18 groups and 7 periods. 1
- Mendeleev left a gap for an element he called eka-aluminium. This element was later discovered as Answer: D. gallium Eka-aluminium is gallium; eka-silicon is germanium and eka-boron is scandium. 1
- According to the modern periodic law, the properties of elements are a periodic function of their Answer: D. atomic numbers Moseley's modern periodic law: properties of elements are a periodic function of their atomic numbers. 1
- Newlands' law of octaves states that the properties of Answer: B. every eighth element are similar to those of the first Newlands arranged elements in increasing atomic mass and found that every... 1
- An element has the electronic configuration 2, 8, 2. Its position in the modern periodic table is Answer: D. group 2, period 3 Three shells means period 3; two valence electrons means group 2. The element is magnesium. 1
- On going down a group in the modern periodic table, the atomic radius Answer: B. increases A new shell is added at each step down a group, so the atomic radius increases. 1
- Which of the following elements of the third period has the highest metallic character? Answer: B. Na Metallic character decreases from left to right across a period, so sodium (group 1) is the most metallic. 1
- The element with atomic number 17 belongs to Answer: C. group 17 Configuration 2, 8, 7: 7 valence electrons in the p-block place it in group 17 (halogens). It is chlorine. 1
- The temperature at which water vapour in the air begins to condense into droplets is called the Answer: B. dew point At the dew point, the air becomes saturated and vapour condenses as dew. 1
- The SI unit of the power of a lens is Answer: B. dioptre Power P = 1/f with f in metres; its unit is the dioptre (D). 1
- Myopia (near-sightedness) is corrected by using a Answer: B. concave lens In myopia the image forms in front of the retina; a concave lens of suitable power moves it back onto the retina. 1
- The image formed on the retina of the human eye is Answer: A. real and inverted The eye lens is convex and forms a real, inverted image on the retina; the brain interprets it as erect. 1
- The power of a convex lens of focal length 50 cm is Answer: D. +2 D P = 1/f = 1/0.5 m = +2 D. 1
- A lens has power −2.5 D. It is a Answer: C. concave lens of focal length 40 cm f = 1/P = 1/-2.5 = -0.4 m = -40 cm. A negative power means a concave lens. 1
- The impression of an image persists on the retina for about Answer: D. 1/16 second This persistence of vision lasts about 1/16 s. 1
- The near point of a normal human eye is at a distance of about Answer: D. 25 cm A normal eye sees clearly objects as close as about 25 cm. 1