Explanation

• Atoms of the same element with different numbers of neutrons are called isotopes.
• Atoms of the same element have the same number of protons and electrons but different numbers of neutrons.

Explanation

Vexing means پریشان کرنے والا

Annoying means غصہ دلانے والا

Disturbing means پریشان کن

Explanation

Sonar (Sound Navigation and Ranging) uses sound waves to detect and locate objects underwater.

It works by emitting sound pulses into the water

And listening for the echoes that bounce back from objects like submarines, fish, or the seafloor.

Sonar is commonly used in navigation, fishing, and underwater exploration.

Explanation

Engrossed means مشغول

Absorbed means جذب

Explanation

If he works hard, he will pass the examination

This is a first conditional sentence

"If + present simple, will + base form of the verb". 

Explanation

Bragged means شیخی مار

Boasted means گھمنڈ

Explanation

He goes to college daily in time.

The subject "He" is third person singular, so in the present simple tense, we add -s to the verb. 

The sentence describes a habitual action, so the present simple tense is appropriate.

Explanation

The phenomenon where a chemical element exists in multiple crystalline forms is called allotropy

Allotropy refers to the ability of an element to exist in two or more different forms in the same physical state.

This is different from polymorphism, which is a broader term referring to any substance (not just elements) that can exist in multiple crystalline forms. 

Explanation

The weight of a man in an elevator descending with an acceleration of 4.9 m/s² will become:

Let:

• Actual weight $W=mg$

• Acceleration due to gravity g=9.8m/s^2

• Acceleration of the elevator a=4.9m/s^2

When an elevator descends with acceleration $a$, the apparent weight becomes:

W′=m(g−a)

Substitute values:

W′=m(9.8−4.9)=m(4.9)
W′=1​/2×mg

So, the apparent weight becomes half of the actual weight.

Explanation

The formula for calculating the density of an ideal gas is d = PM/RT, where: 

• d: is the density of the gas
• P: is the pressure of the gas
• M: is the molar mass of the gas
• R: is the ideal gas constant
• T: is the temperature of the gas in Kelvin

The ideal gas law is expressed as PV = nRT, where 'n' is the number of moles.

Density (d) is mass (m) divided by volume (V), so d = m/V.

We can relate the number of moles (n) to mass (m) and molar mass (M) using n = m/M.

Substituting this into the ideal gas law, we get PV = (m/M)RT.

Rearranging the equation to solve for density (d = m/V), we get d = PM/RT.