Atomic Number and Mass Number | Structure of the Atom | Assessment | English | Grade 9

Which of the following is true?

• An atom must always have a proton, neutron and electron.

• An atom can have only electrons and neutrons but no proton.

• The number of protons are equal to number of electrons.

• The number of neutrons cannot be more than 2.

Answer explanation

the number of protons are equal to the number of electrons.

Tags

NGSS.MS-PS1-1

The isotopes of an element contains _______________ .

• same number of neutrons but different number of protons

• same number of neutrons but different number of protons

• different number of protons as well as different number of neutrons

• different number of neutrons but same number of protons

Answer explanation

Isotopes are defined as the atoms of the same element having the same atomic number but different mass numbers. So, isotopes have the same number of protons in the nucleus but different numbers of neutrons in the nucleus.

The radioactive isotope used in the treatment of cancer is ___________ .

• Cobalt-60

• Plutonium

• Radium

• Iodine-131

Answer explanation

The radioactive isotope used in the treatment of cancer is cobalt-60

Tags

NGSS.HS-PS1-8

Isobars are elements ____________________________ .

• having different atomic numbers but same mass number

• having different mass numbers

• have same number of neutrons

• none of the above

Answer explanation

Isobars are elements of different atoms with different atomic numbers but same mass number.

Mass number is

• Equal to the sum of atomic number and number of neutrons

• Equal to the sum of number of protons and number of neutrons

• Only 1

• Both 1 and 2

Answer explanation

Mass number is equal to the sum of number of protons (atomic number) and number of neutrons

The number of electrons in an atom are 8 and the number of protons are also 8. What is the charge on the atom?

• 0

• 1

• 2

• 3

Answer explanation

Since the number of protons and neutrons are equal, the charge is 0.