BLE Model Paper 1

Two-factor authentication (2FA): besides the password, the account asks for a second proof, a code sent to her phone, which the thief doesn’t have.

Because it can multiply only inside a living host cell, using the cell’s materials and machinery; outside a cell it shows no signs of life.

The variety among individuals of the same species, caused by differences in their genes; for example, the many varieties of rice grown in Nepal.

Layering: a low branch with a ring of bark peeled off is bent down into the soil and covered; when roots have grown from the buried part, it is cut from the parent and planted.

Air (oxygen). The water filled the spaces in the soil, so the seeds couldn’t get the oxygen their cells need for respiration.

So that when the switch is off, the appliance is cut off from the live supply: no part of it is at a high voltage, and nobody touching it gets a shock.

The physical and chemical properties of elements are a periodic function of their atomic numbers.

Lime (calcium hydroxide) or wood ash. It is a base, so it neutralizes the extra acid in the soil.

• i.A testable guess, for example: “Salt makes ice melt faster.” (The opposite, “Salt makes no difference to how fast ice melts”, is also a hypothesis the test can check.)
• ii.Any one: the size of the ice cubes; the kind of plate; the place where they are kept (the same room, both in or out of the sun); the time at which he starts.

• i.Microorganisms need water to grow. Drying removes the water, so molds and bacteria can’t grow on the gundruk, and it keeps for months without rotting.
• ii.The oil covers the pickle and the airtight lid keeps the air, with the germs and mold spores in it, from reaching the pickle, so it doesn’t spoil.

No, I don’t agree.

• a.In in-situ conservation (national parks, conservation areas), the plants and animals live naturally in their own habitat, interacting with the soil, water, climate and other living things, and all the species of the area are protected together.
• b.Ex-situ conservation is laborious and costly: the food and surroundings must be managed every day, only a small number can be kept, and wild animals dislike a prison-like life in a cage. It suits best the species that are endangered, not every plant and animal.

Any two:

• a.The qualities of a known good plant can be copied: the new plants are like the parent.
• b.The new plants bear fruit sooner than plants grown from seed.
• c.Many identical plants can be grown from one parent plant in a short time.
• d.Plants with no viable seeds, such as banana, seedless grapes and pineapple, can still be grown.

• i.Ultrasound (ultrasonic sound), of frequency above 20 kHz (20,000 Hz).
• ii.The sound goes down and comes back up, so

$$\text{depth} = \frac{\text{speed} \times \text{time}}{2} = \frac{1500 \times 3}{2} = 2{,}250\ \text{m}$$

• i.Breaking the magnet doesn’t change how its molecular magnets are lined up. Each piece still has rows of molecular magnets all pointing the same way (open chains), so each has a north pole at one end and a south pole at the other.
• ii.Heating makes the molecular magnets vibrate harder and harder; the shaking breaks up their rows, and they fall back into random directions and closed chains, whose poles cancel.

i. Zinc + hydrochloric acid → zinc chloride + hydrogen
$$\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$$
ii. Hydrogen. A burning splinter brought to the mouth of the tube makes the gas burn with a pop.

• i.They hit the air at very high speed (11 to 72 km/s), so they are heated until they glow and burn up high in the air, 80 to 100 km above the ground, as meteors.
• ii.The Moon has no air, so even small meteoroids hit its surface and blast out craters, and with no wind, rain or living things the craters stay for billions of years. On the Earth, the air burns up the small ones, and weather, water and moving crust have worn away most of the old craters.

• i.Identity theft: he used her name and photo to pretend to be her and cheat others.
• ii.Respect intellectual property: he copied and shared copyrighted material (the film) without permission.
• iii.No. Cybercrime is a serious crime, punished by law. In Nepal, the Electronic Transactions Act, 2063 punishes computer fraud (up to 2 years in prison, a fine of up to Rs 1 lakh, or both), and the Copyright Act, 2059 protects creative work such as films.
• iv.Any one: keep screenshots of the account and the messages; tell her parents or teacher; report the fake account to the social media site and warn her friends not to send money; report it to the Cyber Bureau of Nepal Police.

• i.First-class lever, because the fulcrum (the stone) is between the load (the rock) and the effort (Dawa’s hands).
• ii.Load distance L.D. = 0.3 m; effort distance E.D. = 1.8 m − 0.3 m = 1.5 m. By the principle of the lever,

$$E \times \text{E.D.} = L \times \text{L.D.} \quad\Rightarrow\quad E = \frac{900 \times 0.3}{1.5} = 180\ \text{N}$$

• iii.$$\text{MA} = \frac{L}{E} = \frac{900\ \text{N}}{250\ \text{N}} = 3.6$$
• iv.$$\text{VR} = \frac{\text{E.D.}}{\text{L.D.}} = \frac{1.5}{0.3} = 5, \qquad \eta = \frac{\text{MA}}{\text{VR}} \times 100\% = \frac{3.6}{5} \times 100\% = 72\%$$

• i.A vacuum has no particles, so heat can’t cross it by conduction or convection.
• ii.Shiny, silvered surfaces are poor emitters and reflect the heat rays back, so they reduce the loss of heat by radiation.
• iii.Cork and plastic are poor conductors of heat, and the stopper stops hot air from escaping at the top by convection (and stops evaporation).
• iv.Yes. The same parts stop heat from the outside getting in by conduction, convection and radiation, so the cold water stays cold.

• i.Sulphur, symbol S.
• ii.16 protons and 16 neutrons in the nucleus; 16 electrons in three shells: 2 in K, 8 in L and 6 in M (2, 8, 6).

• iii.2: it has 6 valence electrons and gains 2 to make 8 (8 − 6 = 2).
• iv.Group 16 (6 valence electrons) and period 3 (3 shells).