Explanation

The correct preposition with "concerned" in this context is "about", meaning to be worried or aware of something.

Example: We should be concerned about climate change and its effects.

Explanation

Given that x = 3 is a solution to the equation:

x² + rx - 20 = 4

Substitute x = 3 into the equation:

(3)² + r(3) - 20 = 4

Simplify:

9 + 3r - 20 = 4

Combine like terms:

3r - 11 = 4

Add 11 to both sides:

3r = 15

Divide by 3:

r = 5

Explanation

To evaluate the expression, follow the order of operations:

Multiply 3 and 3: 3 × 3 = 9

Divide 9 by 3: 9/3 = 3

Add 3 and 3: 3 + 3 = 6

Explanation

The conjugate acid of water (H₂O) is H₃O⁺ (hydronium ion).

When water acts as a base, it accepts a proton (H⁺) and forms H₃O⁺.

Explanation

The absolute value | -12 | represents the distance of -12 from zero, which is always positive.

Therefore, | -12 | = 12.

Explanation

The Widal test is used to diagnose Typhoid fever.

It detects antibodies against Salmonella typhi and Salmonella paratyphi, the bacteria responsible for typhoid.

It is a serological test that checks for agglutination (clumping) of bacteria in response to specific antigens.

Explanation

A glucoside bond (glycosidic bond) is a type of covalent bond that links sugar molecules in disaccharides and polysaccharides.

Lactose, a disaccharide, consists of glucose and galactose joined by a β-1,4-glycosidic bond.

Explanation

NH₄Cl (Ammonium chloride) contains three types of chemical bonds:

• Covalent bond → Between N (Nitrogen) and H (Hydrogen) in the NH₄⁺ (Ammonium ion).
• Coordinate (Dative) bond → Between N and one of the H atoms, where nitrogen donates a lone pair.
• Ionic bond → Between NH₄⁺ (Ammonium ion) and Cl⁻ (Chloride ion).

Explanation

Substitute n = 3 into the expression: 2²(3) + 17

Simplify the exponent: 2⁶ + 17

Calculate 2⁶: 64

Add 17: 64 + 17 = 81

Explanation

To convert 0.50% to a fraction:

0.50% = 0.50/100

= 0.0050

To simplify:

0.0050 = 5/1000

= 1/200