Explanation

The refractive index of glass typically ranges from 1.5 to 1.9, depending on the type of glass.

Standard crown glass has a refractive index of approximately 1.5.

Explanation

Valency is the number of electrons an atom can gain, lose, or share to achieve a stable configuration.

Carbon (C) has an atomic number of 6, with an electron configuration of 2,4.

It needs 4 more electrons to complete its outer shell (octet rule), so its valency is 4.

Explanation

"The number of" is a singular subject, so it takes a singular verb.

"Is" is the correct verb because it agrees with the singular subject "The number".

Explanation

To compare fractions, convert them to decimal values:

7/9 = 0.777

5/6 = 0.833

8/9 = 0.888

8/7 = 1.142

The smallest value among them is 7/9.

Explanation

Rhombic sulphur and monoclinic sulphur coexist at 95.5°C, known as the transition temperature.

Below 95.5°C, rhombic sulphur is stable, while above it, monoclinic sulphur is more stable.

Explanation

Speed of light in air (or vacuum) is approximately 3 × 10⁸ m/s (299,792,458 m/s), which is the fastest speed possible in nature.

Light slows down in denser mediums like water or glass due to interactions with particles, but in air, it remains very close to its speed in a vacuum.

Explanation

Given k = 15:

(k-2) = 15 - 2

= 13

Now, calculate 180/k:

180/k = 180/15

= 12

Multiply (k-2) by 12:

13 × 12 = 156

Explanation

Given that the sum of 3, 7, and x is 18:

3 + 7 + x = 18

Combine constants:

10 + x = 18

Subtract 10 from both sides:

x = 8

Now, find the average (arithmetic mean) of 3, 7, and x:

Average = (3 + 7 + x) / 3

= (3 + 7 + 8) / 3

= 18 / 3

= 6

Explanation

Bile is a digestive fluid produced by the liver and stored in the gallbladder, but it does not contain digestive enzymes.

Instead, bile contains bile salts, which help emulsify fats, making them easier for enzymes like lipase to break down.

Explanation

Since a 20% discount reduced the price to Rs. 100:

x - (20% of x) = 100

To find 20% of x, multiply x by 0.20:

x - 0.20x = 100

Combine like terms:

0.80x = 100

Divide by 0.80:

x = 125