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Phenolphthalein is a synthetic indicator and its colours in acidic and basic solutions, respectively are (a) red and blue. (b) blue and red. (c) pink and colourless. (d) colourless and pink

Answer: (d) colourless and pink Synthetic indicators are compounds created in a chemistry lab rather than compounds found in nature. Examples of... View Article

Products of a neutralisation reaction are always (a) an acid and a base. (b) an acid and a salt. (c) salt and water. (d) a salt and a base.

Answer: (c) salt and water. A neutralization reaction can be defined as a chemical reaction in which an acid and base quantitatively react... View Article

The correct way of making a solution of acid in water is to (a) add water to acid. (b) add acid to water. (c) mix acid and water simultaneously. (d) add water to acid in a shallow container.

Answer: (b) add acid to water. If we add water to acid it will be an exothermic reaction which will produce a lot of heat which may lead to... View Article

Look at Figure. The length of wire PQ in case of A is equal to the diameter of the semicircle formed by the wire CDE, in case B. One pin is attached to each wire with the help of wax as shown in Figure 4.9. Which pin will fall first? Explain.

Answer: Because CDE > PQ, the pin on the wire in case A will fall first because heat will reach it before the pin in case B. Heat is... View Article

Observe the picture given in Figure. Water is being boiled in a pan of wide base. Which position P or T will feel warmer? Fill up the boxes P and T to indicate the mode of flow of heat to the hand.

Answer: (1) Position ‘P’ will feel warmer due to rising up of hot air. (2) P Convection T Radiation Convection - Convection is the... View Article

At a campsite, there are tents of two shades – one made with black fabric and the other with white fabric. Which one will you prefer for resting on a hot summer afternoon? Give a reason for your choice. Would you like to prefer the same tent during winter?

Answer: In summer I would choose a tent with white colour fabric as white is a bad absorber and a good reflector of Heat. But in winter I would... View Article

Why is it advised not to hold the thermometer by its bulb while reading it?

Answer: When reading a thermometer, it is recommended that we do not hold it by its bulb because the mercury in the bulb will expand owing to... View Article

You may have noticed that a few sharp jerks are given to clinical thermometer before using it. Why is it done so?

Answer: The jerks applied to the thermometer before use in order to obtain an accurate reading allow the mercury level to flow into the bulb... View Article

For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places, where room temperature remains much below the range, the setting of curd becomes difficult. Suggest a way to set curd in such a situation.

Answer: In order to maintain the desired temperature container with curd should be wrapped with woollen or any other insulator. Curd can also be... View Article

In the arrangements, A and B shown in Figure, pins P and Q are fixed to a metal loop and an iron rod with the help of wax. In which case are both the pins likely to fall at different times? Explain.

Answer: Pins in fig B are more likely to fall apart at different times, whereas pins in fig A are more likely to fall apart at the same... View Article

A circular metal loop is heated at point O as shown in Figure (i) In which direction would heat flow in the loop? (ii) In which order the pins at points P,Q and R fixed with the help of wax fall if points O, P, Q and R are equidistant from each other?

Answer: (i) Heat flows in solids at the same rate in all directions, hence heat will flow from O to P and likewise from O to R.(ii)The heat... View Article

In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?

Answer: Mercury gets expanded on heating, hence its level rises in the capillary when comes in contact with a hot object. In a mercury... View Article

To keep her soup warm Paheli wrapped the container in which it was kept with a woollen cloth. Can she apply the same method to keep a glass of cold drink cool? Give a reason for your answer

Answer: Yes, the woolen cloth can be used to keep a glass of cold drink cool because woollen is an insulator that will not allow escape or entry... View Article

A laboratory thermometer A is kept 7 cm away on the side of the flame while a similar thermometer B is kept 7 cm above the flame of a candle as shown in Figure Which of the thermometers, A or B, will show a greater rise in temperature? Give a reason for your answer.

Answer: (B) Because the air near the candle heats up and rises due to convection, thermometer B will receive more heat than thermometer A.... View Article

Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.

Answer: (c) Jute is an insulating substance that prevents ice from melting too quickly. So, while selling ice blocks, retailers frequently wrap... View Article

Figure (a–d) shows the readings on four different thermometers. Indicate which of the reading shows the normal human body temperature?

Answer: (c) A thermometer is a device used for measuring temperature. This ice-covered thermometer shows that the temperature is about 0 degrees... View Article

Fig (a–d) shows a student reading a doctor’s thermometer. Which of the figure indicates the correct method of reading temperature?

Answer: (a) A thermometer is a device used for measuring temperature. This ice-covered thermometer shows that the temperature is about 0 degrees... View Article

Four arrangements to measure the temperature of the ice in a beaker with laboratory thermometer are shown in Figure (a, b, c and d). Which one of them shows the correct arrangement for accurate measurement of temperature?

Answer: (a) A thermometer is a device used for measuring temperature. This ice-covered thermometer shows that the temperature is about 0 degrees... View Article

Boojho has three thermometers as shown in Figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose? (a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water. (b) Thermometer (i) for measuring the temperature of both. (c) Thermometer (ii) for measuring the temperature of both. (d) Thermometer (iii) for measuring the temperature of both.

Answer: (a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water. Image (i) and (iii)... View Article

Paheli and Boojho measured their body temperature. Paheli found her’s to be 98.6 °F and Boojho recorded 37°C. Which of the followng statement is true? (a) Paheli has a higher body temperature than Boojho. (b) Paheli has a lower body temperature than Boojho. (c) Both have a normal body temperature. (d) Both are suffering from fever.

Answer: (c) Both have a normal body temperature. Degree Celsius and Fahrenheit are two scales of temperature measurement. Normal body temperature... View Article

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