Question

For which of the following orbital wave function does not change its sign at any distance from the nucleus?

• A. 3d
• B. 2p
• C. 2s
• D. 1s

Answer 1

The correct option is D 1s

The $1s$ orbital is spherical because the value of square of wave function at a given distance from the nucleus is same in all directions. The value of the function changes with distance from nucleus, but sign do not change.
The $2p$ orbital has two lobes. The sign of wave function within one lobe is opposite to the sign of wave function in the other lobe. So, we place a plus sign in one lobe and minus sign in other lobe. The value of wave function is zero at the node located between the two lobes of $2p$ orbital.