Which sensor in a smartphone is responsible for switching the display between portrait and landscape when the phone is turned?

The correct answer is A, Long Term Evolution. LTE is the radio access technology of fourth generation mobile networks, standardised by the Third Generation Partnership Project. The name records the intention of the standard bodies to let the existing GSM and UMTS networks evolve over the long term towards an all-IP system rather than be replaced overnight, and voice over LTE later brought ordinary calls on to the same data network. Option B, Last Time Evolution, is not a term used anywhere in telecommunications. Option C, Least Time Evolution, is likewise invented and has no technical meaning. Option D, Long Time Evolution, is the commonest wrong choice because it differs from the right answer by a single word, but the standard uses the word term, not time. Candidates should remember LTE with 4G and New Radio with 5G.

The correct answer is B, duplexing. A telephone conversation requires both parties to speak and listen at the same time, so a mobile link must carry traffic in both directions together. That arrangement is called duplexing, and cellular systems achieve it either by using two separate frequency bands, known as frequency division duplex, or by alternating very rapidly between sending and receiving on one band, known as time division duplex. Option A, triplexing, is not a recognised mode of mobile communication. Option C is wrong because the correct term for one-way communication is simplex, not simplexing, and a simplex link such as a broadcast cannot support a phone call. Option D, quadraplexing, is not a term in mobile standards at all. Only duplex and its two forms appear in the syllabus of cellular communication.

The correct answer is A, Subscriber Identity Module. The SIM is a small smart card issued by the operator that stores the subscriber identity, the authentication keys used to prove that identity to the network, and a limited amount of contact and message data. Because the identity lives on the card, a subscriber can move the number to another handset simply by moving the card. Option B, Single Identity Module, resembles the right answer but is not the standard expansion. Option C, Subscriber Internet Module, is wrong because the card is not tied to internet service; it authenticates voice, message and data service alike. Option D, Secure Identity Memory, is invented, although the card is indeed a secure element. Note the contrast with the IMEI, which identifies the handset rather than the subscriber.

The correct answer is C, 15. The International Mobile Equipment Identity is a fifteen-digit number assigned to every handset, made up of a code identifying the type approval of the model, a serial part and a final check digit. It can usually be displayed by dialling a short code and is printed under the battery or on the box. Because it identifies the device rather than the subscriber, it is the number quoted when a lost phone is reported so that the network can bar the handset. Option A, ten digits, is the length of an Indian mobile telephone number, which is why it is the commonest wrong answer. Option B, twelve digits, is the length of the Aadhaar number. Option D, twenty digits, matches the longer identifier printed on some SIM cards, not the IMEI.

The correct answer is B, Linux. Android uses a modified Linux kernel at its lowest layer to manage memory, processes, power and device drivers, and builds its own runtime, libraries, application framework and user interface above it. The project began at a company called Android Inc., which Google acquired in 2005, and the first Android handset reached buyers in 2008. Option A is wrong because the Windows NT kernel underlies desktop Windows and the discontinued Windows Mobile line, not Android. Option C is wrong because kernels derived from Unix and BSD underlie Apple macOS and iOS, which are Android competitors rather than its base. Option D is wrong because Symbian was a complete mobile operating system of the era before Android, used mainly by Nokia, and it was never a kernel for Android.