4. which statement gives you enough
information to say that the atom is
electrically neutral?
o a. the atom has 7 protons and 7
electrons.
ob. the atom has 4 neutrons and 4
protons.
o c. the atom has 19 electrons and 19
neutrons.
od. the atom has 15 neutrons and 15
electrons.

The atom having 7 protons and 7 electrons is electrically neutral.

Explanation:

There are 3 subatomic particles present in an atom. They are: protons, electrons and neutrons

Atomic number is defined as the number of protons or number of electrons present in a neutral atom. It is represented by Z.

Z = Atomic number = Number of electrons = Number of protons.

Mass number is defined as the sum of number of protons and number of neutrons present in an atom. It is represented as A.

A = Mass number = Number of neutrons + Number of protons.

For an atom to be electrically neutral, the atom must have equal number of protons and electrons.

Hence, the atom having 7 protons and 7 electrons is electrically neutral.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.