1. Check statement (a)

For a given principal quantum number $n$, orbitals with higher azimuthal quantum number $l$ generally have electron density farther from the nucleus compared to lower $l$ orbitals.

Example: for the same shell, $s < p < d < f$ in penetration, so higher $l$ means less penetration and the electron tends to stay farther away.

So, (a) is true.

2. Check statement (b)

The statement says:

For a given value of principal quantum number, the size of the orbit is inversely proportional to the azimuthal quantum number.

This is not correct. In wave mechanics, electrons are described by orbitals, not fixed orbits. Also, orbital size is not simply inversely proportional to $l$.

So, (b) is false.

3. Check statement (c)

According to wave mechanics, orbital angular momentum is given by

$L = \sqrt{l(l+1)}\,\frac{h}{2\pi}$

For the ground state of hydrogen, the electron is in the $1s$ orbital, so $l=0$. Thus,

$L = \sqrt{0(0+1)}\,\frac{h}{2\pi}=0$

So ground state angular momentum is not $\dfrac{h}{2\pi}$.

Hence, (c) is false.

4. Check statement (d)

For plots of wavefunction $\psi$ versus radial distance $r$ for different azimuthal quantum numbers, the maxima shift toward larger $r$ as $l$ increases (for a given $n$). This reflects that higher-$l$ orbitals are more concentrated farther from the nucleus.

So, (d) is true.

5. Select the correct combination

True statements are:

$(a), (d)$

Therefore, the correct option is:

$\boxed{\text{B}}$