Flowering can be induced in pineapple by application of

The correct option is NAA, 2,4-D.

Explanation:
Pineapple (Ananas comosus) is a commercial fruit crop where uniform flowering and fruit set are critical for synchronized harvesting. In agricultural practice, plant growth regulators are widely used to induce and align the flowering process.

Auxins are a class of plant hormones that play a key role in regulating growth and development, including flowering. Specifically, synthetic auxins such as:
1. NAA (Naphthalene acetic acid)
2. 2,4-D (2,4-Dichlorophenoxyacetic acid)
are highly effective in triggering flowering in pineapple plants when applied at optimal concentrations.

While natural auxins like IAA (Indole-3-acetic acid) also play a role in plant development, synthetic auxins like NAA and 2,4-D are preferred in agriculture due to their stability and high potency in inducing flowering in pineapple. Therefore, the combination of NAA and 2,4-D is the correct treatment for flowering induction in pineapples.