Atrue statement about mass is that:
(a.) mass is often measured with a spring scale
(b.) mass is expressed in pounds
(c.) as the force of earth's gravity on an object increases, the object's mass increases
(d.) mass is determined by comparing the mass of an object with a set of standard masses that are part of a balance

(c.) as the force of Earth's gravity on an object increases, the object's mass increases

Explanation:

Based on newton's law of gravitation "every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them".

It is mathematically expressed as:

    F =

F is the gravitational force on either particle

m₁ and m₂ are the masses

r is the distance between particles

G is the universal gravitation constant.

From this expression, we see that the force of earth's gravity is directly proportional to mass.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.  

because natural gas is colorless, odorless, and tasteless, distributors add mercaptan (a chemical that smells like sulfur) to give natural gas a distinct unpleasant odor (it smells like rotten eggs). they locate the types of rock that are likely to contain natural gas deposits.