CDS 2018 Previous Year GK Questions with Answers

The correct answer is C, Magnesium. A magnesium atom sits at the centre of every chlorophyll molecule, so a plant cannot make chlorophyll without it.

Chlorophyll is built around a ring-shaped structure called a porphyrin, with a single magnesium ion held at its centre. This is the pigment that absorbs red and blue light and gives leaves their green colour. When magnesium is short, older leaves turn yellow between the veins, a condition called chlorosis. A similar ring with iron at the centre forms haem, the part of haemoglobin that carries oxygen in our blood, a pairing examiners like to test.

A is wrong: calcium builds cell walls (as calcium pectate) and helps cell division, but it is not part of chlorophyll.

B is wrong: iron is needed for the enzymes that help make chlorophyll, yet it is not in the chlorophyll molecule; magnesium is.

D is wrong: potassium controls the opening and closing of stomata and activates enzymes, but has no place in chlorophyll.

Exam tip: chlorophyll has magnesium at its centre; haemoglobin has iron; vitamin B12 has cobalt.

The correct answer is B, magnesium carbonate and hydrochloric acid. A carbonate reacts with an acid at room temperature to give carbon dioxide, and only carbon dioxide turns limewater milky.

The reaction is MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂. The fizzing comes from carbon dioxide escaping. When this gas is passed through limewater, a solution of calcium hydroxide, it forms insoluble calcium carbonate, which makes the water look milky: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. If more carbon dioxide is passed for a long time, the milkiness disappears as soluble calcium hydrogen carbonate forms. Every carbonate and hydrogen carbonate behaves this way with acids.

A is wrong: zinc and hydrochloric acid give hydrogen gas, which burns with a pop but does not affect limewater.

C is wrong: methane and oxygen do not react at room temperature; they need a flame to burn.

D is wrong: copper is below hydrogen in the reactivity series and does not react with dilute hydrochloric acid at all.

Exam tip: metal + acid gives hydrogen (pop test); carbonate + acid gives CO2 (limewater test).

The correct answer is D, Sixth Schedule. It provides for Autonomous District Councils in the tribal areas of Assam, Meghalaya, Tripura and Mizoram, and is read with Article 244(2). These councils are elected bodies that can make laws on land, forests, village administration, inheritance, marriage and social custom, run their own courts for tribal disputes and levy certain taxes, which gives the four states a measure of self-rule unlike anywhere else in India. The Bodoland Territorial Council in Assam and the Khasi Hills council in Meghalaya are well-known examples. Option A is wrong because the Third Schedule only contains the forms of oath and affirmation for the President, ministers, judges and legislators. Option B is wrong because the Fourth Schedule allots Rajya Sabha seats to the states and union territories. Option C is wrong because the Fifth Schedule governs scheduled areas in the other states through a Governor and a Tribes Advisory Council, not elected district councils. Exam tip: Fifth Schedule for scheduled areas elsewhere, Sixth Schedule for the four north-eastern states.

The correct answer is 91st Amendment. The 91st Amendment Act, 2003 inserted Article 75(1A), which says the total number of ministers, including the Prime Minister, in the Union Council of Ministers shall not exceed 15% of the total number of members of the Lok Sabha, and Article 164(1A), which applies the same limit to the States, with a minimum of 12 ministers. It also barred a member disqualified for defection from being appointed a minister, and strengthened the anti-defection law by deleting the provision that allowed "splits".

The other amendments are from around the same time but on different subjects. The 97th Amendment (2011) dealt with co-operative societies. The 87th Amendment (2003) provided for delimitation of constituencies on the basis of the 2001 census. The 90th Amendment (2003) concerned representation in the Assam Legislative Assembly from the Bodoland Territorial Areas District. The 15% cap was meant to stop jumbo ministries formed to reward supporters and hold coalitions together.