Energy Technologies and Storage

• Statement 1 is correct and states the fundamental distinction between the two routes. Photovoltaic conversion is a quantum process: a photon of energy greater than the band gap generates an electron-hole pair in a semiconductor and the built-in field of the p-n junction separates the carriers, producing current without any intermediate thermal or mechanical stage. Solar thermal conversion is a heat-engine process: concentrating collectors raise a working fluid to high temperature, and the heat is converted to work in a Rankine or Brayton cycle and thence to electricity, so it is subject to the Carnot limit in a way photovoltaics is not.
• Statement 2 is incorrect, and is the inversion of the truth. A photovoltaic cell is a direct-current device; the current flows one way across the junction, and an inverter is needed before the output can be fed to the grid. Solar thermal plants drive a conventional synchronous turbo-alternator and therefore produce alternating current natively.
• Statement 3 is incorrect. In 2014 India had a substantial and long-established photovoltaic manufacturing base in cells and modules, dating to the 1980s, while its solar thermal manufacturing capability was thin and most concentrating solar power components for the Jawaharlal Nehru National Solar Mission projects were imported. The statement reverses the position. The official answer is therefore (a).
• Statement 2 is the decisive one and is settled by physics alone, with no recall of Indian industry required: rejecting it removes (b) and (c), and statement 1 is manifestly true, which removes (d).

• Statement 1 is correct. A hydrogen fuel cell oxidises hydrogen electrochemically rather than by combustion: hydrogen is oxidised at the anode, the electrons travel through the external circuit, and at the cathode oxygen combines with them and with the protons that have crossed the electrolyte to form water. Since the free energy change is not fully converted to electrical work, the balance appears as heat, so water and heat are the only by-products, and the absence of carbon in the fuel is why there is no carbon dioxide.
• Statement 2 is incorrect. Fuel cells scale across the whole range, from megawatt stationary installations down to portable units; direct methanol fuel cells were developed precisely for laptops and handheld devices, and the statement's restriction is false.
• Statement 3 is incorrect and is the cleanest elimination in the item. A fuel cell is an electrochemical cell and produces direct current by its nature, since the electrode reactions fix the polarity; an inverter must be added to supply alternating current to a grid or a building. The official answer (a) follows. Elimination route: the direct current point alone removes options (b), (c) and (d), so a candidate secure on that single fact answers the item without judging the other two statements.

• Statement 1 is incorrect. India has almost no capacity in the upstream stages of the photovoltaic value chain. That chain runs from polysilicon to ingots, then wafers, then cells, then modules, and Indian manufacturing is concentrated almost entirely at the module assembly end, with limited cell capacity and effectively no commercial polysilicon, ingot or wafer production. China dominates wafer manufacture with a share above ninety per cent, and it is precisely this dependence on imported cells and wafers that prompted the safeguard duty debate of 2018 and the later production linked incentive scheme for solar modules.
• Statement 2 is incorrect and turns on the distinction between discovering a price and determining a tariff. The Solar Energy Corporation of India is a central public sector undertaking under the Ministry of New and Renewable Energy that acts as an implementing agency and an intermediary offtaker; it conducts reverse auctions in which developers bid, and the winning bid establishes the price. Determination and adoption of tariffs is a regulatory function vested in the Central Electricity Regulatory Commission and the State Electricity Regulatory Commissions under the Electricity Act, 2003, which adopt a competitively discovered tariff or fix one where there has been no competitive bidding. Both statements failing, the answer is (d). Elimination route: statement 2 rewards the general principle that in the Indian power sector the entity that runs a procurement is not the entity that regulates a tariff, and statement 1 rewards awareness that India imports the great bulk of its solar hardware.

Hence (d).

The reasoning here is first principles rather than recall. Solar photovoltaic panels supply electricity, and once electricity is available the pump does not know or care where it came from. What the panel constrains is the power available and its variation through the day, not the type of pump.

• Statement 1 is therefore incorrect, and solar submersible pumps are in fact the commoner configuration in India because groundwater tables lie below the suction limit of a surface pump.
• Statement 2 is incorrect for the same reason. Centrifugal pumps are usual because they suit continuously variable speed drives, but positive displacement pumps including piston and helical rotor types are used with solar arrays, and they are preferred at low flow and high head. Neither statement stands, giving (d).
• Options (a), (b) and (c) all treat the energy source as though it dictated the mechanical design.

All three describe established or demonstrated uses of hydrogen, and green hydrogen differs from other hydrogen only in its production route, namely electrolysis powered by renewable electricity, not in its end use chemistry.

• Statement 1 is correct, hydrogen internal combustion engines having been demonstrated in cars, buses and generator sets, burning hydrogen in a modified spark ignition engine.
• Statement 2 is correct, hydrogen being blended into natural gas grids at low percentages for heating and power, with trials in India and abroad.
• Statement 3 is correct, the proton exchange membrane fuel cell producing electricity directly from hydrogen and oxygen with water as the only exhaust, which is the basis of fuel cell electric vehicles. Hence (c). The question is generous in that each option is a well publicised application, and no elimination is needed.

In a proton exchange membrane fuel cell, hydrogen is oxidised at the anode to protons and electrons, the protons cross the membrane, the electrons do external electrical work, and at the cathode oxygen combines with protons and electrons to form water. The only tailpipe product is therefore water, emitted chiefly as vapour along with warm air, which is why these vehicles are described as zero emission at the point of use.

• Option (a) is wrong because hydrogen peroxide can appear only as a transient and undesirable intermediate from incomplete oxygen reduction, and it is a degradation problem for the membrane rather than an emission.
• Option (b) is wrong because the hydronium ion exists within the hydrated membrane as the proton carrier and is not emitted.
• Option (c) is wrong because oxygen is consumed as the oxidant at the cathode, not produced.

Pumped storage hydropower uses surplus off peak or surplus renewable electricity to pump water from a lower reservoir to an upper reservoir, and releases it through turbines when demand or price is high. It is the dominant form of grid scale long duration energy storage worldwide, offering discharge over many hours and a service life measured in decades, which is why it is central to integrating variable solar and wind generation.

• Option (a) is wrong because terraced field irrigation is a soil and water conservation practice with no storage and generation cycle.
• Option (b) is wrong because lift irrigation pumps water for agricultural use and does not recover the energy, so it is a consumer rather than a store of electricity.
• Option (d) is wrong because rainwater harvesting captures precipitation for water supply and recharge, with no energy dimension at all. The distinguishing feature of pumped storage is that the pumping energy is deliberately recovered.

In a lithium-ion cell the cathode is a lithium metal oxide and the anode is almost always graphite, and this division is the whole content of the question. Cobalt, lithium and nickel are cathode constituents: the dominant chemistries are nickel manganese cobalt oxide and nickel cobalt aluminium oxide, alongside lithium iron phosphate which dispenses with nickel and cobalt, and lithium is present in every cathode formulation since it supplies the ions that shuttle during cycling. Graphite is the anode material, chosen because its layered structure intercalates lithium ions reversibly between graphene planes at a potential close to that of lithium metal without the dendrite formation that plagues lithium metal anodes. Three elements therefore belong to the cathode, giving (c).

• Option (d) requires graphite to be counted as a cathode material, which reverses the electrode assignment.
• Options (a) and (b) understate, and would require excluding one of the three genuine cathode elements. The practical significance is that cobalt and nickel supply concerns drive cathode chemistry away from cobalt-rich formulations, while graphite supply is a separate and equally concentrated bottleneck on the anode side.

• Statement I is correct: the scheme, launched in February 2024 and implemented by the Ministry of New and Renewable Energy, targets the installation of rooftop solar systems in one crore residential households, supported by central financial assistance graded by system capacity and by collateral-free concessional loans, with households receiving free electricity up to a specified monthly consumption and able to sell surplus power to the distribution company.
• Statement II is correct: the scheme provides for training at grassroots level in installation, operation, maintenance and repair of rooftop solar systems, which addresses the practical constraint that a dispersed residential rollout of this scale needs a distributed technician base rather than a few large contractors.
• Statement III is correct: the capacity building component envisages the creation of more than three lakh skilled personnel through fresh skilling and upskilling, with a substantial share as certified solar photovoltaic technicians. All three hold, giving (d).
• Options (a), (b) and (c) each drop one accurate component. The design point worth noting is that the scheme couples a demand-side subsidy with a supply-side skilling programme, since installation capacity rather than panel availability is usually the binding constraint on rooftop deployment.

• Statement 1 is incorrect and is the eliminator, because hydrogen produced by steam methane reforming with the resulting carbon dioxide captured and stored is blue hydrogen. The feedstock remains a fossil fuel and the emission reduction depends on the capture rate, so it is not green by definition. Green hydrogen is defined by the origin of the energy, not by the treatment of the exhaust.
• Statement 2 is correct and is that definition, namely electrolysis of water driven by renewable electricity, which yields hydrogen and oxygen with no carbon in the process chain at all.
• Statement 3 is correct, since the National Green Hydrogen Mission approved in January 2023 carries the stated targets of about five million tonnes of annual production capacity by 2030 together with abatement of nearly fifty million tonnes of greenhouse gas emissions a year.

Hence 2 and 3 and (b) is correct, while (a) and (d) accept the blue hydrogen description and (c) drops the mission target.