Periodic Classification of Elements — Science STD 10 — Question

Evolution of cauliflower, broccoli, cabbage, red cabbage has occurred from wild cabbage. Is this an example of natural selection or artificial selection?

Anannya responded to the question: Why do electrical appliances with metallic bodies are connected to the mains through a three pin plug, whereas an electric bulb can be connected with a two pin plug?
She wrote: Three pin connections reduce heating of connecting wires.
(i) Is her answer correct or incorrect? Justify.
(ii) What is the function of a fuse in a domestic circuit?

Name two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table. In what manner do they change?

Which gas is usually liberated when an acid reacts with a metal? How will you test for the presence of this gas?

A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads:
Left eye: +2.50D, Right eye: +2.00D

1. State whether these lenses are thicker in the middle or at the edges.
2. Which lens bends the light rays more strongly?
3. State whether these spectacle lenses will converge light rays or diverge light rays.

What is baking soda? Write the chemical name of baking soda. Give the important uses of baking soda. How does baking soda differ chemically from washing soda?

If a potential difference of 10V causes a current of 2A to flow for 1 minute, how much energy is transferred?

The magnification of an image formed by a lens is – 1. If the distance of the image from the optical centre of the lens is 35 cm, where is the object placed ? What is the nature and focal length of the lens? If the object is displaced 20 cm towards the optical centre of the lens, where would the image be formed and what will be its nature? Draw a ray diagram to justify your answer.

Why, we do not use series combination of connecting electric appliances in household circuit?

Name the functional group of organic compounds that can be hydrogenated. With the help of suitable example explain the process of hydrogenation mentioning the conditions of the reaction and any one change in physical property with the formation of the product. Name any one natural source of organic compounds that are hydrogenated.